# 67 GTO Stalls at Idle While Braking



## armyadarkness (Dec 7, 2020)

I finally got my car running like an animal. Low end, mid, and top are perfect, however the car jumps all over at idle and the minute that you put it in gear, it dies. Reverse seems worse than drive. The vacuum is great and I've checked all of the hoses for leaks. Fuel pressure is perfect, carb is new, plugs are white, plug wires are new. Dizzy/ cap/ rotor/ coil are new, but I'm going to replace the cap, rotor, and coil tonight (most likely).

Would anything obvious cause this? It wasn't this way a week ago and then it started to do it (again). When I bought the car it did this, but I gave it a tune up and replaced the carb and it went away.

Could the vacuum modulator at the trans be leaking? It doesnt seem like it is. It seems to get worse as the car warms up, but it's too soon to tell. It's only in the 30's here.


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## armyadarkness (Dec 7, 2020)

And... for anyone familiar with my setup, this wouldn't be the cam, would it? I recall it not being any more radical than on OEM RA cam.


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## deanhickey (Apr 6, 2015)

Shouldn't be the cam, but with out the specs it's hard to say. When you set the idle mixture screws did you use a vacuum gauge or by RPM, not that it makes a lot of difference in my opinion but try it the other way and see how it does at idle. To me it sounds like you are running a little lean. Then look at your timing maybe too much advance. these are all shots in the dark without knowing more.


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> Shouldn't be the cam, but with out the specs it's hard to say. When you set the idle mixture screws did you use a vacuum gauge or by RPM, not that it makes a lot of difference in my opinion but try it the other way and see how it does at idle. To me it sounds like you are running a little lean. Then look at your timing maybe too much advance. these are all shots in the dark without knowing more.


My cam specs are posted in another thread here. I figured that most of the regulars here had already seen them, not long ago. The general consensus was that they were mild. 

I set the mixtures with a vacuum gauge, for best vac, and then "try" to lean out a bit for the plugs to stay clean. I have bad OCD, so then I check it with a tach, too... Then I also have an AFR gauge, so I see it daily. It's definitely lean at idle. 16-17 on the AFR.

Timing is right at 12 and 34-36 total. 

I'm going to do some more testing tonight. I just wanted a second set of eyes/ ears on it.


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## armyadarkness (Dec 7, 2020)

Bullet Cam part no. 507000 

The specs for the cam appear to be 222/230, 353/353, 530/530


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## michaelfind (Dec 14, 2018)

How much is it jumping around RPM wise? Where does it idle in Park?


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## armyadarkness (Dec 7, 2020)

michaelfind said:


> How much is it jumping around RPM wise? Where does it idle in Park?


Havnt installed the interior tach yet, so I don't know. Tonight I'll check spark at the plugs (AGAIN), then reset the idle mixtures, and check the rpms


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## armyadarkness (Dec 7, 2020)

Like I said, I've checked everything multiple times, but I find that with stuff like this, two heads are better than one. You never know when someone will say "same thing happened to me. It was a bad shift modulator".


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## deanhickey (Apr 6, 2015)

armyadarkness said:


> Bullet Cam part no. 507000
> 
> The specs for the cam appear to be 222/230, 353/353, 530/530


Do you have the Lobe separation angle, as this has a huge impact on idle. My cam has an LSA of 116.0 ( I think) the narrower you go the lumpier it gets and idle suffers, I remember reading that below 114.00 it will be very lumpy/rough and the overlap increases.


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> Do you have the Lobe separation angle, as this has a huge impact on idle. My cam has an LSA of 116.0 ( I think) the narrower you go the lumpier it gets and idle suffers, I remember reading that below 114.00 it will be very lumpy/rough and the overlap increases.


I do. Let me see... If what you're saying is true, then it looks like that's an issue. It definitely sounds like it has a lopey cam... But in my case, that usually means that I have a straight six with a spark plug wire wrapped around the steering. So, I guess sitting in gear with foot on brake, power brake booster, isn't helping. It does seem to be better sometimes and suck others. Will a vac can help? I never had a cam worth mentioning.


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## armyadarkness (Dec 7, 2020)

So... Maybe keeping it lean at idle and the RPS at 700, is not a great idea with this cam.


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## Old Man Taylor (May 9, 2011)

You LSA is 110. Try setting the idle to 1000 RPM and see what happens.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> You LSA is 110. Try setting the idle to 1000 RPM and see what happens.


Thanks J! I know it will improve dramatically, but I thought it was bad for an auto to idle so high.


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## armyadarkness (Dec 7, 2020)

This cam is like Pandora's box. I guess it's a great cam, but it definitely makes a terrible "mystery cam"!


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## armyadarkness (Dec 7, 2020)

As I keep mentioning, off idle, cruise, and top end power are crazy good.


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## armyadarkness (Dec 7, 2020)

I just talked to the guys at Bullet, and they shot holes in our LSA theory. They said that in order for that to hurt, I'd have to have much more radical duration. They did agree that the carb and ignition are likely intact, because the car makes great power everywhere else.

They did recommend bumping up idle RPM to at least 850. I set my idle using lean drop, I think I should reverse that as well.


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> Do you have the Lobe separation angle, as this has a huge impact on idle. My cam has an LSA of 116.0 ( I think) the narrower you go the lumpier it gets and idle suffers, I remember reading that below 114.00 it will be very lumpy/rough and the overlap increases.


The guy at Bullet seemed well versed in the old Ram Air cams. I can tell that he was an old school rodder. He said that the RA cams had a 113.5 LSA, so that they would idle with their giant duration. I've never gotten into cam specs. I know nothing.


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## PontiacJim (Dec 29, 2012)

Timing is at 12 with vacuum advance disconnected, right? Connect the vacuum line and it should jump up to around 21-22 at idle.

I would set my idle based on what the RPM drop is. This is where a higher stall converter is needed to give the converter more slip at idle and when braking. If you have to use more than light brake pedal pressure to hold your car from taking off on you, the converter is too tight. With that cam, I would want my idle in Drive at around 750 RPM's.

Your idle A/F is too lean in my opinion. Get it to 13.5-14. Bigger cam can use a little richer mixture.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> Timing is at 12 with vacuum advance disconnected, right? Connect the vacuum line and it should jump up to around 21-22 at idle.
> 
> I would set my idle based on what the RPM drop is. This is where a higher stall converter is needed to give the converter more slip at idle and when braking. If you have to use more than light brake pedal pressure to hold your car from taking off on you, the converter is too tight. With that cam, I would want my idle in Drive at around 750 RPM's.
> 
> Your idle A/F is too lean in my opinion. Get it to 13.5-14. Bigger cam can use a little richer mixture.


Great advice on the TC and AFR. I wouldnt know to treat this car any different. I keep the plugs clean by idling lean! And I have to stand on the brakes to keep the car from taking off at idle! Thanks Jim


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## Old Man Taylor (May 9, 2011)

My point was to set it at something that works first, and then finesse it to what it will stand.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> My point was to set it at something that works first, and then finesse it to what it will stand.


Yes I know. I also found out another juicy, relevant tidbit yesterday!!!!

At the bottom of my cam card, there is a number, which I never understood; AFO18736542

When I explained to the guys at Bullet, how I chased my tail because there was no Four/ Seven swap indicator on the paperwork... That's it! The number stands for "Alternate Firing Order 18736542". I can't believe that this doesn't come up as an issue, more often.


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## armyadarkness (Dec 7, 2020)

For the record, what is a good rpm for a stall speed converter, for my car? When the engine was built, they did the trans and a shift kit, but there's no mention of a converter, so I'll assume that it's stock. Of course, now that I have discovered I can use my console with a Tremec, I'm near certain that I'll convert it.


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## michaelfind (Dec 14, 2018)

armyadarkness said:


> For the record, what is a good rpm for a stall speed converter, for my car? When the engine was built, they did the trans and a shift kit, but there's no mention of a converter, so I'll assume that it's stock. Of course, now that I have discovered I can use my console with a Tremec, I'm near certain that I'll convert it.


You would have to pull the transmission to change the torque converter. At that point, you might as well do your transmission change. Also, I believe that choosing a TC is like choosing camshafts, there are lots of things to consider (and everybody is an expert in his own mind). I suggest that you make the best of what you have for now, and begin gathering parts to make the change to standard transmission as soon as possible.


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## lust4speed (Jul 5, 2019)

Were you running your plug wires 18436572 on a cam for 18736542? If so, what happened when you swapped #4 and #7 wires to match the cam? Seems like that is a big enough deal they should have that in bright red ink and yellow highlighter. Can't figure out why anyone would do the swap on a mild cam, but then again I've never been a proponent of the swap.

Before reading that I was thinking something much more boring like you were running manifold vacuum advance and sometimes the combination of mechanical advance and full time vacuum can create a cliff. Engine is happy at idle with having a little mechanical advance and also kicking in some vacuum advance at say 800 RPM in park, and then you drop it in gear and that's enough to drop vacuum and drop mechanical and engine now isn't happy. Sort of like falling off a cliff where a very slight drop in RPM triggers an increasing drop as mechanical and vacuum go away and it spirals on down in RPM.

Easiest cure would be to swap over to ported vacuum. While the engine is going to need more throttle to initially maintain a set idle, it won't be nearly as prone to dropping out when put in gear. Second part of the cure that you might not need is to insure the distributor is curved where the mechanical advance doesn't start to move until a few hundred RPM over idle speed. You should be able to check for both vacuum and mechanical influences on idle by using the timing light while someone drops the car in gear. With the car as it is I would expect to see the timing fall from 24° or so down to the basic timing or close to it.


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## Montreux (Mar 8, 2009)

A slightly looser torque converter will let the car idle in gear without being so “loose” that it creates a lot of heat in the transmission. I have used a 

Hughes GM25-BPO

and loved it. Just loose enough to let it get up on the cam when you hammer it.

I’ve never used an AFR gauge, but I think you want it on the rich end of the scale at idle. After you get it rich enough for stable idle using the mixture screws and idle speed screw, pull the carb and look to see if the idle transfer slot is overly exposed. If so, you need to increase the idle air. On a Rochester, there is a passage through the body that can be drilled bigger (see Cliff Ruggles’ book). Alternately, a small hole can be drilled near the edge of the butterfly above the idle transfer slot. (This was done at the factory for some RA cars). Fine tune the mixture with the car in gear.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> Were you running your plug wires 18436572 on a cam for 18736542? If so, what happened when you swapped #4 and #7 wires to match the cam? Seems like that is a big enough deal they should have that in bright red ink and yellow highlighter. Can't figure out why anyone would do the swap on a mild cam, but then again I've never been a proponent of the swap.
> 
> Before reading that I was thinking something much more boring like you were running manifold vacuum advance and sometimes the combination of mechanical advance and full time vacuum can create a cliff. Engine is happy at idle with having a little mechanical advance and also kicking in some vacuum advance at say 800 RPM in park, and then you drop it in gear and that's enough to drop vacuum and drop mechanical and engine now isn't happy. Sort of like falling off a cliff where a very slight drop in RPM triggers an increasing drop as mechanical and vacuum go away and it spirals on down in RPM.
> 
> Easiest cure would be to swap over to ported vacuum. While the engine is going to need more throttle to initially maintain a set idle, it won't be nearly as prone to dropping out when put in gear. Second part of the cure that you might not need is to insure the distributor is curved where the mechanical advance doesn't start to move until a few hundred RPM over idle speed. You should be able to check for both vacuum and mechanical influences on idle by using the timing light while someone drops the car in gear. With the car as it is I would expect to see the timing fall from 24° or so down to the basic timing or close to it.


Yep... I bought the car with a fresh rebuild, had all of the paperwork, but none of it stated 4/7 swap. Previous owner never heard of a 4/7 swap and he wasn't aware of it. Googlin the cam made no mention of it. Old Man Taylor mentioned the 4/7 to me, and in my 35 years of Pontiacing, that was the first that I had heard of it. However, like you, he didn't think that they wouldve used one for such a mild cam. 

So for a week, I fought that issue.

Finally, Pontiac Jim came across something, which indicated that it was the 4/7. I too found the same thing on a Chevelle site. I switched the wires and it solved the issue.

Now it's running rough and jumping forward at idle. I checked the plugs and they're great, so I made a new set of MSD 8.8's, and that didn't do it. It seemed ignition related, but the car made great power, doing everything, except idling in P or R. So, I went after vacuum, last night.

The PCV grommet was the original, so I replaced it, and wow... that seemed to help right away. The difference between the worn one and new, was stellar. Then, I moved the brake booster hose from the front of the carb to the rear, that also seemed to help. I moved the PVC from the manifold to the front of the carb. The initial timing seemed too advanced, so I backed that off, reset the mixtures with a tach and vac gauge, to just at 15 at 850 RPM's, and now my AFR gauge reads low 14 at idle.

As I left it idle for almost an hour, and with my cooling system mods, it never went over 140 and it FINALLY sounded smooth out of the tail pipes. 850 is higher than I like for an idle, but it's not slamming into gear when I shift. I may lower it to see if I can, but I'm definitely going to continue cleaning up my vacuum line routing.


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## armyadarkness (Dec 7, 2020)

Montreux said:


> A slightly looser torque converter will let the car idle in gear without being so “loose” that it creates a lot of heat in the transmission. I have used a
> 
> Hughes GM25-BPO
> 
> ...


Typically, and there are many schools of thought/ preferences here, you want the idle on the lean side so that the plugs stay clean. That's why GM cars listed the "Lean Drop" method of setting the mixtures, on all of their emission labels. I did richen it last night, so we'll see if it helps.


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## armyadarkness (Dec 7, 2020)

armyadarkness said:


> s I left it idle for almost an hour, and with my cooling system mods, it never went over 140 and it FINALLY sounded smooth out of the tail pipes. 850 is higher than I like for an idle, but it's not slamming into gear when I shift. I may lower it to see if I can, but I'm definitely going to continue cleaning up my vacuum line routing.


I SPOKE TOO SOON...

The issue does not arise until after 5 minutes of driving. Temp never goes over 140 at idle and 160 under hard use. I bought the car on December 15 and it ran "okay", but after a bit it died, in gear, when idling. Later, the previous owner revealed that he knew about it.

I replaced the OEM dizzy with HEI, new plugs, MSD 8.8 wires, new vacuum lines and rerouted, new coil, new carb, air filter, a fuel pressure regulator. It still exhibits the same behavior. Runs like a clock, strong as Hell, mid range and WOT are epic, dies at a stop sign with my foot on the brake.

Here's what I've narrowed it down to:

Torq converter: In 60 cars and 35 years, I never saw one go bad. Do they? If so, is it a condition that worsens with heat? This only occurs after 5 minutes of normal driving.
Choke: It is electric, easy enough to test. I caught it staying closed on my vette, but would I be able to do 30 foot posi burnouts at 20MPH, if the choke was closed?
Fuel filter: Is the AC with return line, and I can see that it's installed backwards. I also found a hole in the return line. I will be changing this, but in the meantime, I have a Holley pressure regulator after this and it's reading 5.5, which is what I need. If I was having a fuel delivery issue, would I be able to do 30 foot posi burnouts at 20MPH and then scramble to 120MPH?
Cap and rotor: On my second set. The originals were points with 200 miles on them, now it's HEI. The current ones did go through the 4/7 swap debacle, so I dont know if the incorrect firing order would've stressed them. If they were bad, would I be able to do 30 foot posi burnouts at 20MPH and then scramble to 120MPH?
Coil: Same as cap and rotor.
Brake booster: This booster is an aftermarket from a disc brake conversion. COuld it be consuming all of my vacuum at idle? If so, why only after the car has run for 5 minutes and only when in gear... not with foot on brake in Park or neutral.
Intake manifold: Ive repeatedly checked for leaks and found none. However, when I was younger, I bought a Pontiac Edelbrock at a swap meet, and when I got home, I found out that it was cracked. I later had a similar issue on another Pontiac. I never knew why, but now that I know about the exhaust crossover, I suspect that it what caused the cracks in both of those old manifolds. Has anyone else had this happen? If so, a crack in aluminum is definitely something that would open and worsen with heat. Could an exhaust crack share realestate with an intake runner? If so, then that's definitely a vacuum leak that would worsen as the car warmed up, but wouldnt it also kill my mid WOT power?
This is an issue that only appears after 5 minutes of normal driving, in drive or reverse, while idling with foot on brake. 

*CRITICAL NOTES:*

I currently have the vacuum advance sharing a vacuum line with the TH400 shift modulator, and going to the manifold vacuum port on the carb.
I changed the oil with full synthetic, less than 200 miles ago, and it's black. The motor only has about 1000 miles on it.


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## deanhickey (Apr 6, 2015)

armyadarkness said:


> I SPOKE TOO SOON...
> 
> The issue does not arise until after 5 minutes of driving. Temp never goes over 140 at idle and 160 under hard use. I bought the car on December 15 and it ran "okay", but after a bit it died, in gear, when idling. Later, the previous owner revealed that he knew about it.
> 
> ...


I know this sound over simplified but I would change the fuel filter, I had the same symptoms with my Saab and it turned out to be the fuel filter. It's a cheap procedure and will just eliminate on more possible area. Good luck.


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## deanhickey (Apr 6, 2015)

deanhickey said:


> I know this sound over simplified but I would change the fuel filter, I had the same symptoms with my Saab and it turned out to be the fuel filter. It's a cheap procedure and will just eliminate on more possible area. Good luck.


I know it may sound counter intuitive, but think what your fuel pump is doing at low revs, it is just sipping from the tank. Amy obstruction could reduce fuel flow, at higher revs the pump is sucking harder and is able to pull the required fuel through the lines. If you have a gauge on your regulator warm up the engine till the symptoms appear then have some one put it in gear with foot on the brake and watch your fuel pressure. I would also chock the wheels and have someone you trust in the car.


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> I know this sound over simplified but I would change the fuel filter, I had the same symptoms with my Saab and it turned out to be the fuel filter. It's a cheap procedure and will just eliminate on more possible area. Good luck.


I'll take whatever help I can get. Last resort is to pull the intake, and I JUST flushed and replaced that entire system, so I'm not looking to mess with it unless I HAVE to. Fuel filter is definitely doable... I wouldve done it already, but since I found the leaking line, I was stalling until I could do both. However, all it does is cool the fuel, so for now, I'll eliminate the return and just replace the filter with a single in/ out


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> I know it may sound counter intuitive, but think what your fuel pump is doing at low revs, it is just sipping from the tank. Amy obstruction could reduce fuel flow, at higher revs the pump is sucking harder and is able to pull the required fuel through the lines. If you have a gauge on your regulator warm up the engine till the symptoms appear then have some one put it in gear with foot on the brake and watch your fuel pressure. I would also chock the wheels and have someone you trust in the car.


Yeah, that's why it's so hard to diagnose. I'm alwasy alone and I need to drive the car, warm it, and then have it in gear with foot on brake... not easy to do... alone, without an ebrake, on a car that's jumping around and dying, with a sharp, new, flex fan! thanks for the idea's. I need em all!

Could the TH 400 modulator be stealing vac advance?


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> I know this sound over simplified but I would change the fuel filter, I had the same symptoms with my Saab and it turned out to be the fuel filter. It's a cheap procedure and will just eliminate on more possible area. Good luck.


BTW, I could see that happening, but I would think it would do it cold, too.


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## deanhickey (Apr 6, 2015)

armyadarkness said:


> BTW, I could see that happening, but I would think it would do it cold, too.


It wouldn't start happening until I drove a few miles in my case, I rebuilt the ignition system and replaced a few sensors before the light went on in my head. It wouldn't hurt to change the filter then see. you would eliminate one of the possibilities. As far as vacuum goes it would happen at the high end not at idle as vacuum drops at higher rpm. if you have a good brake pedal at high rpm after pumping it a few times the vacuum should be fine. What kind of pedal do you have at idle? Do you have a vacuum canister?


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## armyadarkness (Dec 7, 2020)

deanhickey said:


> It wouldn't start happening until I drove a few miles in my case, I rebuilt the ignition system and replaced a few sensors before the light went on in my head. It wouldn't hurt to change the filter then see. you would eliminate one of the possibilities. As far as vacuum goes it would happen at the high end not at idle as vacuum drops at higher rpm. if you have a good brake pedal at high rpm after pumping it a few times the vacuum should be fine. What kind of pedal do you have at idle? Do you have a vacuum canister?


The brake pedal is awesome, without pumping, all of the time. I could be doing 70 and stand on the brakes and it stops like a charm. Agreed that the questionable filter is a no-brainer to try, just not optimistic that it's the issue.

Yous say "As far as vacuum goes it would happen at the high end not at idle as vacuum drops at higher rpm". I assume you mean "wouldn't" not would?

No I don't have a vacuum reserve can, but I do recall needing to install one on my old 67, back in 1995. I wouldve only done that if the brakes were depleting the vacuum. Do brake boosters steal enough vacuum to kill fuel delivery at idle? I can easilly weld a few ports on a can and install it to try. Is that needed? Did Ram Air cars or non hideaway cars have them?


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## deanhickey (Apr 6, 2015)

armyadarkness said:


> The brake pedal is awesome, without pumping, all of the time. I could be doing 70 and stand on the brakes and it stops like a charm. Agreed that the questionable filter is a no-brainer to try, just not optimistic that it's the issue.
> 
> Yous say "As far as vacuum goes it would happen at the high end not at idle as vacuum drops at higher rpm". I assume you mean "wouldn't" not would?
> 
> No I don't have a vacuum reserve can, but I do recall needing to install one on my old 67, back in 1995. I wouldve only done that if the brakes were depleting the vacuum. Do brake boosters steal enough vacuum to kill fuel delivery at idle? I can easilly weld a few ports on a can and install it to try. Is that needed? Did Ram Air cars or non hideaway cars have them?


I don't think it is your break booster but would check it for leeks, if it was stealing vacuum you would have reduced braking power at high rpm due to the loss of vacuum supplied by the engine and at idle you would feel a change in your break pedal as vacuum decreased. do you have fuel mixture gauge on the car? If it is the filter you should see a drop in mix ratio when you put it under load at idle speed. Your choke is keeping the mixture richer until it opens and then you have a lean condition and the carb can't supply enough fuel. In park there is a lot less demand for fuel so it would run easily when put into gear the rpms drop and the fuel pump slows down by up to 20% in some cases. Just spitballing at this point.


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## armyadarkness (Dec 7, 2020)

I do have an AFR gauge and at idle, it's now low to mid 14. I haven't checked it during "the condition", to see if it changes.


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## ylwgto (Oct 27, 2009)

I had a similar issue a few moths ago (horrible idle, running rich, dying out in gear). I thought it was electrical and changed out all my plugs, wires and coil...still no change and almost replaced my MSD box. Then I found this and realized it was a carb issue:






I know you have an Edelbrock, but perhaps it is a similar issue with your electric choke? On my Holley it took me 3 times to adjust it properly so that my car didn't die at start up due to improperly positioned butterflys. 

Also, as others have said, I'd bump up your curb idle screw a bit, then work back until you find a good idle RPM when you drop it into gear. 

Not sure the vacuum advance and trans modulator should be sharing a line or if one would rob the other of vacuum at idle vacuum. if you have another port on the carb available, its easy enough to give them dedicated lines. 

I had to change my fresh oil out after I diagnosed this because it was also black and washed with gas from the rich condition. Does your oil smell like gas?


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## lust4speed (Jul 5, 2019)

Black oil: Pistons 4 and 7 cycle the same so each are coming up to their top dead center at the same time. Cam determines valve action, and on a standard cam profile 4 is coming up on compression and 7is pushing the mixture out and distributor fires #4 at this time. When the wires are swapped the spark occurs just after the cylinder is evacuated. Lots of wasted fuel that isn't ignited going out the exhaust and unburned fuel gets by the rings and ends up down in the crankcase. At least the spark occurs on an empty cylinder and not that bad of result. Swap some other wires and you can have spark with the piston coming up and have massive detonation. While not that great of thing for ring and oil life there's no harm to the ignition system.

Swapped wires will have engine running on 6 cylinders and power should be way off. An easy check would be to pull power to HEI and crank engine with a finger over one of the holes until pressure is felt. At that point pull the cap and see if rotor is pointing towards 4 or 7. Doesn't have to be that precise since 4 and 7 terminals they are on opposite sides of the distributor. It just has me worried that you said engine idled rougher after swapping wires.

When the car dies at warm idle, does it start right back up and do you have normal power if you get on the gas right after an event? I probably missed it, but what type of fuel pump requiring the regulator? Have a friend that had a problem with dying after warming up at idle but his problem was an electric pump that puts out 12+ PSI and a regulator that finally went bad. The regulator needle and seat were allowing pressure creep when sitting at a light. In 15 to 20 seconds at idle pressure would built up to the carb and was raising the float level until his carb would flood out. Driving down the street the problem wasn't really noticeable.


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## armyadarkness (Dec 7, 2020)

ylwgto said:


> I had a similar issue a few moths ago (horrible idle, running rich, dying out in gear). I thought it was electrical and changed out all my plugs, wires and coil...still no change and almost replaced my MSD box. Then I found this and realized it was a carb issue:
> 
> 
> 
> ...


Thanks for reading!

Electric Choke procedure for Holley and Eddy are the same, and they're deceptively difficult to set "right". My vette was set all wrong, so the choke never opened all of the way and I lost tons of power. Yes it wreaks of gas, yet the plugs are very clean.

Eddy carbs only have two ports, one timed and one full... Since the vac advance should be on full, I doubt the shift modulator should be timed, that's why I piggy backed them. I don't know how the shift modulator works, but if it needs full vac at idle, in gear, then maybe a 3/16 line, shared with the vac can, isn't enough? The line off the trans is 5/16 I think, so that would indicate that it needed a lot of vac. I have open manifold ports, so I can try that.

I already tried the idle... As for start up, it starts and idles fine, so it's not likely the choke. I can put it in gear, indefinite, with my foot on the brake, with no issue, so long as I never actually drive it. After I drive it for 5 minutes, then when I stop, it dies.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> It just has me worried that you said engine idled rougher after swapping wires.
> 
> When the car dies at warm idle, does it start right back up and do you have normal power if you get on the gas right after an event? I probably missed it, but what type of fuel pump requiring the regulator? Have a friend that had a problem with dying after warming up at idle but his problem was an electric pump that puts out 12+ PSI and a regulator that finally went bad. The regulator needle and seat were allowing pressure creep when sitting at a light. In 15 to 20 seconds at idle pressure would built up to the carb and was raising the float level until his carb would flood out. Driving down the street the problem wasn't really noticeable.


The cam is a 4/7 swap and with the wires right, now it idles perfect.

When the car dies at idle, it's ONLY after it has been run on the road for 5 minutes, in Reverse or Drive, with foot on brake. In the driveway, it'll never do it. When it dies on the road, yes it starts right back up, and if I pin the gas, it'll roast the tires and go sideways.

I have the stock mechanical fuel pump, but an Edelbrock carb and they're finicky with anything over 5.5 psi, so I never run them without a regulator and gauge. However, even though I'm a self proclaimed Edelbrock carb expert, I never had one on a car with a fuel tank return, AND I just found a small leak in the return line.

Could it be possible that it's 5.5 at idle, but then pressure drops when I get on it, because fuel is going back to the tank at an accelerated rate, so when I stop, the bowls are now out of gas and the car dies? Seems super unlikely. The fuel filter is also on backwards and probably very old... So that's alarming, however... As I keep questioning "would a car with a backwards fuel filter, and a hole in the return line, do 20 mph posi burn outs, chirp third and then hit 120 mph like a rocket?" 

I can't imagine that happening if I was having a fuel starvation or choke problem. But, tomorrow, I'll replace the filter, fix the return, and then verify the pressure. If that doesn't help, I'll move the shift modulator vacuum line. If that doesnt do it, I'll replace the cap, rotor, and coil. If that doesnt do it, I'll pull the intake and look for cracks. After that, I'll sell the car. I've spent $3000 in a month trying to fix this issue.


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## armyadarkness (Dec 7, 2020)

ylwgto said:


> I had a similar issue a few moths ago (horrible idle, running rich, dying out in gear). I thought it was electrical and changed out all my plugs, wires and coil...still no change and almost replaced my MSD box. Then I found this and realized it was a carb issue:
> 
> 
> 
> ...


Thanks for reading! 

Electric Choke procedure for Holley and Eddy are the same, and they're deceptively difficult to set "right". My vette was set all wrong, so the choke never opened all of the way and I lost tons of power. Yes it wreaks of gas, yet the plugs are very clean.

Eddy carbs only have two ports, one timed and one full... Since the vac advance should be on full, I doubt the shift modulator should be timed, that's why I piggy backed them. I don't know how the shift modulator works, but if it needs full vac at idle, in gear, then maybe a 3/16 line, shared with the vac can, isn't enough? The line off the trans is 5/16 I think, so that would indicate that it needed a lot of vac. I have open manifold ports, so I can try that.


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## deanhickey (Apr 6, 2015)

for 10 dollars just change the filter.


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## armyadarkness (Dec 7, 2020)

I already bought it. It's interesting... When I asked for the filter, they gave me the brass one, because I don't have AC. I told him that it was wrong and so he showed me the AC filter, which is what I have. So... my car had dealer installed air, and I'm amazed at how far the dealer went to match factory AC. The y changed the sender, ran a line, changed the filter, and changed the gears! 

The general consensus is to keep the return line, but none of my other cars had it and they were fine. Now I don't know what to do. Especially since the line has a hole in it. Nothing on this car is easy. I can't believe that i'm actually missing working on the corvette.


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## deanhickey (Apr 6, 2015)

armyadarkness said:


> I already bought it. It's interesting... When I asked for the filter, they gave me the brass one, because I don't have AC. I told him that it was wrong and so he showed me the AC filter, which is what I have. So... my car had dealer installed air, and I'm amazed at how far the dealer went to match factory AC. The y changed the sender, ran a line, changed the filter, and changed the gears!
> 
> The general consensus is to keep the return line, but none of my other cars had it and they were fine. Now I don't know what to do. Especially since the line has a hole in it. Nothing on this car is easy. I can't believe that i'm actually missing working on the corvette.


keep the return line < it helps keep the fuel cool. a leaking return is easy to fix. what do you have for a fuel pump?


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## armyadarkness (Dec 7, 2020)

New return fuel line, new filter, rechecked timing, reset idle mixtures, new cap, rotor, and coil, separated shift modulator and vacuum advance. Test drove it after each change and it does the same thing. Startes right up, idles like a dream, drives terrific for 4 minutes, and then as soon as you stop it dies. Restart it, hit the gas, roast both tires, clean into second, chirp third. Idle at 1000, still no change.


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> New return fuel line, new filter, rechecked timing, reset idle mixtures, new cap, rotor, and coil, separated shift modulator and vacuum advance. Test drove it after each change and it does the same thing. Startes right up, idles like a dream, drives terrific for 4 minutes, and then as soon as you stop it dies. Restart it, hit the gas, roast both tires, clean into second, chirp third. Idle at 1000, still no change.


Bad brake booster or the grommet/check valve going into the booster. Do the grommet/check valve first as its the cheapest.

You should see vacuum drop using a gauge, I would think. Put the car in drive while running and hold your foot on the brake pedal for several minutes to see if you lose vacuum.

Might need to raise idle in gear to something like 900-1,000 RPM's. Try that, even though you'll have to stand on the brakes to stop. Just do the test near the home where you don't have to go far or get up to any real speed. Throw the trans into neutral if you have to help the car stop after the test, or in an emergency stop.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> Bad brake booster or the grommet/check valve going into the booster. Do the grommet/check valve first as its the cheapest.
> 
> You should see vacuum drop using a gauge, I would think. Put the car in drive while running and hold your foot on the brake pedal for several minutes to see if you lose vacuum.
> 
> Might need to raise idle in gear to something like 900-1,000 RPM's. Try that, even though you'll have to stand on the brakes to stop. Just do the test near the home where you don't have to go far or get up to any real speed. Throw the trans into neutral if you have to help the car stop after the test, or in an emergency stop.


This will be my last test before I pull the manifold and replace it, and then the trans. This cam doesn't seem so radical that it would cause idle vac issues, but I only have 15 at idle and they say that's the minimum you need for good idle. So if the booster is evacuating it, that makes sense. Just unusual that the cam company wouldnt have mentioned it when we spoke.

The booster is newer, because the car has a brake conversion. I assume that I can just disconnect the booster, plug the carb, and try it with manual brakes?


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## BearGFR (Aug 25, 2008)

Are you/we still chasing the 'stalls while braking' problem? I don't remember seeing you mention it, and I'm admittedly too lazy to read back through the thread 😜 so, what kind of carb are you running?

Bear


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> Are you/we still chasing the 'stalls while braking' problem? I don't remember seeing you mention it, and I'm admittedly too lazy to read back through the thread 😜 so, what kind of carb are you running?
> 
> Bear


Yep. Stalls when braking from a drive, or while idling in P or R. Edelbrock AVS2 800 carb


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## armyadarkness (Dec 7, 2020)

Also stalls with steering to a full lock, with foot on brake .


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## BearGFR (Aug 25, 2008)

Ok, well that kills where I thought I might be going. If it was 'brand H', hard braking can slosh the fuel to the front of the bowl and uncover the jets and IFR's so that they're just sucking air.


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> Ok, well that kills where I thought I might be going. If it was 'brand H', hard braking can slosh the fuel to the front of the bowl and uncover the jets and IFR's so that they're just sucking air.


I'm hoping that it's the brake booster, stealing the vacuum. It shouldnt be, but that's the best case scenario. Otherwise, I have to pull the intake and pressure test it, and after that, the torq converter will have to get replaced. 

The frustrating part is that when you Google it, there are literally thousands of people with the same issue, and every solution is to replace spark plugs, fuel injectors, and MAP sensor, so it's pretty cool that I'm the only guy on Earth, that ever had this happen with a carburated Pontiac engine! Woooo! I may not have a Judge or an H.O. but I definitely have the rarest car!


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## Greg Hill (Jul 15, 2020)

you need either a looser converter or a smaller cam. Maybe spread out the centerline to a 112 or 114. My car has a similar cam and is right on the borderline of doing the same thing. I have no idea why someone would put a 4/7 swap cam in a street motor.


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## armyadarkness (Dec 7, 2020)

Greg Hill said:


> you need either a looser converter or a smaller cam. Maybe spread out the centerline to a 112 or 114. My car has a similar cam and is right on the borderline of doing the same thing. I have no idea why someone would put a 4/7 swap cam in a street motor.


Lol. Yes... None of us had any idea why anyone would do a 4/7 swap in this car.

I hooked up my vacuum gauge, warmed up the car, threw it in gear and hit the brakes, and dropped to 10hg or below. Can manufacturers recommend a pump or reserve, if it ever drops below 15. If I'm hitting 10 in my driveway, then I'm probably only getting 6 or less, when hitting the brakes from doing 75mph.


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## BearGFR (Aug 25, 2008)

Before you start buying parts and tearing things apart, disconnect and cap off -every- vacuum connection to the engine and see if that changes what you see on a vacuum gauge (which will be the only thing connected). If it has a factory vacuum gauge, disconnect and plug even that ftting and use a hand-held one just in case it turns out that the factory gauge is leaking. If everything is the same, then you know that whatever it is, it's happening because of the engine's personality. If that seems to make thing a lot better, then lather-rinse-repeat while connecting things one at a time until you find the culprit.

I'm no expert on 4/7 swaps, but I don't understand why that would make any difference in the price of frijoles in Tijuana. All that does is change the firing sequence and the air flow direction through the intake. As long as the cylinders are getting filled and firing properly, it doesn't seem like it should matter and/or have much effect on vacuum. Instead of 5/7 firing next to each other, now 4/2 do. My understanding is that the goal is to smooth impulse harmonics on the crank and also to improve/even out air/fuel distribution in the intake tract

4/7 swap - discussion

Seems to me that it ought to make vacuum better, not worse, but like I said, I ain't no expert. 

Bear


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## Old Man Taylor (May 9, 2011)

armyadarkness said:


> Lol. Yes... None of us had any idea why anyone would do a 4/7 swap in this car. - - - - -


I planned on using a new cam in the last build of the 434 in my GTO. When I called to order the cam they said they couldn't get what I wanted in a standard firing order - the cam suppliers were all out of standard blanks. However, they did have blanks with the 4/7 swap. So that's what I now have in my GTO. It wasn't my first choice.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> I planned on using a new cam in the last build of the 434 in my GTO. When I called to order the cam they said they couldn't get what I wanted in a standard firing order - the cam suppliers were all out of standard blanks. However, they did have blanks with the 4/7 swap. So that's what I now have in my GTO. It wasn't my first choice.


The worst part is, I finally got the plug wires to lay all nice on the cap, now they're screwy again! I really have no com[plaints about the cam, but I'm also not thrilled with it. EVERYONE keeps saying that it's mild, yet aparently, I have all of the vacuum and idling woes of a big cam. So... with 10.5 compression and high flow heads on a $5k engine build, I don't see why they didn't put a bigger cam in. And right now, I have yet to see it barely run at all, so I'm rapidly growing to hate the cam.


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> Before you start buying parts and tearing things apart, disconnect and cap off -every- vacuum connection to the engine and see if that changes what you see on a vacuum gauge (which will be the only thing connected). If it has a factory vacuum gauge, disconnect and plug even that ftting and use a hand-held one just in case it turns out that the factory gauge is leaking. If everything is the same, then you know that whatever it is, it's happening because of the engine's personality. If that seems to make thing a lot better, then lather-rinse-repeat while connecting things one at a time until you find the culprit.
> 
> I'm no expert on 4/7 swaps, but I don't understand why that would make any difference in the price of frijoles in Tijuana. All that does is change the firing sequence and the air flow direction through the intake. As long as the cylinders are getting filled and firing properly, it doesn't seem like it should matter and/or have much effect on vacuum. Instead of 5/7 firing next to each other, now 4/2 do. My understanding is that the goal is to smooth impulse harmonics on the crank and also to improve/even out air/fuel distribution in the intake tract
> 
> ...


I will be doing these tests tonight. We've had snow here, and now salt on the roads, so test drives have been off limits, all week.


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## Lemans guy (Oct 14, 2014)

I think you are just too lean on the idle circuit. You said above 14.....Computer assisted FI that runs at 14.7 Stoich is more efficient and the mixture needed is not the same for carbs.

when you idle in your driveway, it will idle forever,....it will at 14+.......but when you drive the throttle opens and the mixture up until 2500 RPM’s or so is the same as idle,....except when you let off the gas......then the AFR will spike lean from the change...and running it at 14+....could push that lean rush up to 16 or more and cause a stall.

I would run your idle mixture at 13.8:and see if that helps. Carbs just don’t adjust as fast as FI, that is why we have accelerator pumps to cover the lean bog you would get when that rush of air goes in......but their is no de-celebrator pump!

Now some cars had that idle plunger contraption anti stall dash pot....that did just that...when you let off the gas the plunger kept the throttle from closing too fast and creating the lean “Stall”......

13.8 is not too rich, carbs will backfire and stall if run too lean. Remember stoich is perfect for emissions,...not power...power requires a richer mixture...like 12.2 on acceleration

try that......I bet you are lean stalling.....


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## Lemans guy (Oct 14, 2014)

Even 13.5 at idle in this cold weather is OK......If your running 10% ethanol pump gas the Stoich on that is 14.1......pure gas 14.7......so you can see where the lean is.....

if this does not help I would definitely watch an AFR meter at the stall point, it could tell you rich or lean......

just some other thoughts for you,....you did not say how much your vac can was pulling on the distributor.....most all of them pull way too much like 20 or 25 degrees....

and with low vacumn the can can either in and out which will effect your timing at idle....as the timing is jumping the engine can stall.....

if you are running a vac can on that HEI let me know, I will tell you which exact one to get so it will pull full timing at low vac and the right amount....they cost about $15...but you may already have that right.

since you had some effect fixing the PCV and grommet some improvement there may really help. All the PCV valves are cheap made in Kathmandu or somewhere and don”T work too good. But it is supposed to be mostly closed at idle and mostly open at Heavy throttle.....if it is open at idle it will mess up your mixture.....maybe after it opens after driving it sticks open, new one or not they are all cheap.....

I use and recommend to everyone with our hot rods the ME Wagner dual flow PCV valve,..check their website. Really improves everything on the engine and dials it in exactly. Even if the PCV is not related to your stalling, this is still a great $150 upgrade that will save you in many ways and you do it yourself.

let us know, I think it is, mixture but could be timing dropping from vac can as well.


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> I think you are just too lean on the idle circuit. You said above 14.....Computer assisted FI that runs at 14.7 Stoich is more efficient and the mixture needed is not the same for carbs.
> 
> when you idle in your driveway, it will idle forever,....it will at 14+.......but when you drive the throttle opens and the mixture up until 2500 RPM’s or so is the same as idle,....except when you let off the gas......then the AFR will spike lean from the change...and running it at 14+....could push that lean rush up to 16 or more and cause a stall.
> 
> ...


After last nights tests, I'm definitely on to your way of thinking. A few others have noted that I should richen up and idle up, but thus far, I couldnt raise the idle high enough to help, and then it slammed into gear... However, with a vac test when holding the brakes in gear at idle, I dropped from 14 to 10. Then, with no vac accessories installed, it did exactly the same thing, so it's obviously not vacuum related (for the most part).

My mixtures are set for the highest vacuum and RPM, when warmed at idle. Tomorrow, I will set them for the highest vacuum, when in gear, with foot on brake.


Lemans guy said:


> Even 13.5 at idle in this cold weather is OK......If your running 10% ethanol pump gas the Stoich on that is 14.1......pure gas 14.7......so you can see where the lean is.....
> 
> if this does not help I would definitely watch an AFR meter at the stall point, it could tell you rich or lean......
> 
> ...


Here's the specs for the dizzy. Proform HEI and I have the can hooked to the FULL vacuum port on the carb.


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## armyadarkness (Dec 7, 2020)

BTW, I sure hope my vac can isn't pulling 20 degrees! I have 12 initial and the mechanical is 22, so that would really suck! How would I check to see what the can is set to?


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## armyadarkness (Dec 7, 2020)

I'm fairly new to messing around with timing, but if I have my dizzy connected to full vac, then at idle, the can isn't even in the picture... Correct?


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## Old Man Taylor (May 9, 2011)

If you use manifold vacuum than it is still in the picture. If you use ported vacuum then it is not. I would disable the vacuum while you're going through this process.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> If you use manifold vacuum than it is still in the picture. If you use ported vacuum then it is not. I would disable the vacuum while you're going through this process.


So... isnt the vac advance initiated when the vacuum drops?


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## Lemans guy (Oct 14, 2014)

So no, let me help you here. I have two Sun Distributor machines and curve distributors often. The first thing I do even on new distributors is to ditch that adjustable vac can that you have. The reason is the can adjusts for rate of vacumn but not total vacumn.nthey pull way too much. Now it can be tempered down with the rate but I don’t use them.

You do want your vac can hooked to full manifold vac,but you want it to pull all the extra timing at idle and low vac......that can you have is probably pulling 20 or more degrees of timing.

Get the can I outline below and just put it in hooked to full manifold vac. It will pull 10 degrees at low vac......it will start pulling at 3 to 6 HG and be totally deployed at 7 to 9 Hg.

well below your 10Hg in drive. It will of course drop out at WOT which will be below 3 Hg.

Now your timing is likely messed up.

All thes cans are made by Standard motor parts, and different parts houses stamp different numbers

Standard Part # SMP VC 302
O’Reilly part # BWD V482
NAPA Part # VC 1703
Rock Auro part # VC 302

put that on and hook to full manifold vac, preferably on a vac line by itself. If your base is 15 this will add 10 at idle, that will be 25 idle timing,...that will idle cool and smooth and vac does noteffect your total timing, as it drops out when Vacumn drops.

I would still run 13.5 to 13.8 and fix this timing! .....


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## Lemans guy (Oct 14, 2014)

The way to check what your current vac can is pulling is just to set the base disconnected. The leave the timing light hooked up and connect the vac line to full manifold vac...now read the timing...you will need a dial back timing light or timing tape to read it.....if it say 35...your vac can is adding 20 degrees to your base.....if it reads 25 it is adding 10 to your base...

the vac can is deployed by high vacumn that is AT idle when it is the highest...that is when you want it at idle and light throttle, that is when you need it to burn the leaner mixtures..


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## Lemans guy (Oct 14, 2014)

It drops out when vacumn drops......


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## Lemans guy (Oct 14, 2014)

Your current vac can may be not only too much,..timing...but is dithering back and forth with the low vacumn, causing erratic timing at idle,

it smooths out as you accelerate because centrifugal timing is “only” RPM related and as you accelerate the vac can has less effect and drops out....

ez fix get that vac can I described.


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> So no, let me help you here. I have two Sun Distributor machines and curve distributors often. The first thing I do even on new distributors is to ditch that adjustable vac can that you have. The reason is the can adjusts for rate of vacumn but not total vacumn.nthey pull way too much. Now it can be tempered down with the rate but I don’t use them.
> 
> You do want your vac can hooked to full manifold vac,but you want it to pull all the extra timing at idle and low vac......that can you have is probably pulling 20 or more degrees of timing.
> 
> ...


I will get the can at NAPA tomorrow!!!! I hope. As for idle mixtures, I intend to adjust them in gear, with foot on brake, for best vacuum. I will then see what my AFR is. Fingers crossed!


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> The way to check what your current vac can is pulling is just to set the base disconnected. The leave the timing light hooked up and connect the vac line to full manifold vac...now read the timing...you will need a dial back timing light or timing tape to read it.....if it say 35...your vac can is adding 20 degrees to your base.....if it reads 25 it is adding 10 to your base...
> 
> the vac can is deployed by high vacumn that is AT idle when it is the highest...that is when you want it at idle and light throttle, that is when you need it to burn the leaner mixtures..


I do use a dial back and I do think it is at 20. I say that because at one point, I think I forgot to disconnect the vacuum when I was setting the timing.


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## armyadarkness (Dec 7, 2020)

I can't get any of those cans before Thursday? What to do in the meantime?


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Your current vac can may be not only too much,..timing...but is dithering back and forth with the low vacumn, causing erratic timing at idle,
> 
> it smooths out as you accelerate because centrifugal timing is “only” RPM related and as you accelerate the vac can has less effect and drops out....
> 
> ez fix get that vac can I described.


Unfortunately, no one has one close.


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> So... isnt the vac advance initiated when the vacuum drops?


No, it's the opposite. The can gets activated when vacuum RISES. When vacuum goes to near zero (like it does at WOT) the vacuum can is completely out of the picture. That's the reason you ALWAYS set initial timing with the can disconnected. You're tuning for best power - WOT - but that's really hard to acheive (read impossible) with the car sitting in your driveway in neutral because there's no load on the engine. If you set timing with the can connected, it's 100% certain that your timing is set WAY too low.

Fix that before you do anything else - do not pass go, do not collect $200

Bewar


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> So no, let me help you here. I have two Sun Distributor machines and curve distributors often. The first thing I do even on new distributors is to ditch that adjustable vac can that you have. The reason is the can adjusts for rate of vacumn but not total vacumn.nthey pull way too much. Now it can be tempered down with the rate but I don’t use them.
> 
> You do want your vac can hooked to full manifold vac,but you want it to pull all the extra timing at idle and low vac......that can you have is probably pulling 20 or more degrees of timing.
> 
> ...


So how does the vac can come into play?

I understand your point about the total degrees and HG at which it hits, but if my initial is 12 and the can is 20, then when the mechanical comes in, wouldn't that be over 50 degrees of timing? I still dont understand the role of the can.

Is it merely to adjust the timing at idle?


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> No, it's the opposite. The can gets activated when vacuum RISES. When vacuum goes to near zero (like it does at WOT) the vacuum can is completely out of the picture. That's the reason you ALWAYS set initial timing with the can disconnected. You're tuning for best power - WOT - but that's really hard to acheive (read impossible) with the car sitting in your driveway in neutral because there's no load on the engine. If you set timing with the can connected, it's 100% certain that your timing is set WAY too low.
> 
> Fix that before you do anything else - do not pass go, do not collect $200
> 
> Bewar


I fixed that weeks ago. The timing seemed off, so I reset it. Tomorrow I will back the can all the way off, until the NAPA can comes in.


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> So how does the vac can come into play?
> 
> I understand your point about the total degrees and HG at which it hits, but if my initial is 12 and the can is 20, then when the mechanical comes in, wouldn't that be over 50 degrees of timing? I still dont understand the role of the can.
> 
> Is it merely to adjust the timing at idle?


 The purpose of the can is to add MORE timing under part-throttle, lightly loaded conditions. Doing that does two things: it helps the engine to run cooler, and also gets better fuel mileage. 

The 'run cooler' part is because at part-throttle, light load conditions the fuel mixture going into the cylinders is 'less dense' -- there's less of it - so when the volume "expands" inside the cylinder the mixture tends to lean out. Lean mixtures take longer to burn, so you need to light the fire earlier to make that happen because otherwise, when the exhaust valve opens that "still on fire" mixture will get pushed out past the valve and into the exhaust ports in the head. That tends to really heat things up and make the engine hotter over all. 

It also means that you're losing the 'benefit' of that fuel burn and heat energy by pumping it out of the cylinder while it's still going instead of using it to turn the crankshaft. That's going to impact fuel mileage because you won't be harnessing as much of the available energy as you could have been.

The solution then, is to "light the fire" earlier under those conditions.

At wide open, heavily loaded conditions though when you've got your big toe hanging over into the carburetor - you don't need nor want that much advance. That much advance on a heavily loaded engine would almost guarantee it would go into detonation - which we know is 'a bad thing'. It just so happens that the amount of manifold vacuum present at any given time is a really good indicator of how hard the engine is working - so that's why it's used to 'vary' the amount of ignition advance.

Bear


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## Lemans guy (Oct 14, 2014)

Timing has 3 modes.

1) the base...set with your hand, fixed never changes bolted down
2) Centrifigal, from weights and springs....only RPM dependent, nothing else 
3) Vacumn advance, load dependent, your foot on the pedal

Total timing is base + Centrifigal.....Vacumnis not figured in because as Bear noted it drops out at WOT.....at wide open throttle you want 36......

But at light throttle cruise you want more than 36...you want 46 to 48 on today’s gas, in the 1960’s you wanted 52 to 54 degrees of timing.....

The reason for this is at light throttle you are only using like 75 or 100 Hp, the mixture is leaner, your throttle is only lightly cracked open....the lean mixture needs more timing advance.....you cannot add more to total or you blow up the engine, but because you can add it with vacumn advance you get a tremendous advantage.

as RPM’s rise Centrifigal timing advances and Vacumn timing decreases, they cross like an X and work at different times......at the lean idle mixtures you want to add extra timing to base.......Vacumn advance allows that to happen, without changing your total timing.


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## Lemans guy (Oct 14, 2014)

And yes it would be over 50 degrees if the can was 20, and that is too much. And most distributors new or old I see have that way too much timing, from both Centrifigal and vacumn.......

Put that can I said on it, hooked to full manifold. If your Centrifigal is 22 set the base at 14 BTDC, That will give you 36 Total.......with the vac can you will have 46 at light throttle cruise and 14 + 10 for 24 degrees of idle timing.....it will idle real smooth and cool there.


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> So how does the vac can come into play?
> 
> I understand your point about the total degrees and HG at which it hits, but if my initial is 12 and the can is 20, then when the mechanical comes in, wouldn't that be over 50 degrees of timing? I still dont understand the role of the can.
> 
> Is it merely to adjust the timing at idle?


The vacuum can on the distributor ONLY works when vacuum is present. When you mash the gas pedal to the floor, engine vacuum goes to near zero, and the vacuum advance drops and this is where your mechanical advance of 12 balancer + 22 distributor = 34, or full mechanical advance, comes into play.

Does the mechanical advance jump right up to 34 degrees when engine vacuum/vacuum can drops to near zero? NO. This is where the mechanical weights in the distributor come into play - they have the springs on them that create your mechanical distributor curve. The 12 degrees at the balancer is a timing constant. Then you mash the gas pedal. Your TOTAL timing at that time is 12 balancer + 16 distributor = 28 full mechanical *+* vacuum advance of 20 = 48 TOTAL advance degrees.

Why 16 distributor and not 22? 22 degrees distributor mechanical is all in at 3,000 RPMs (on our theoretical engine), and you were only at 2,400 RPM's cruising down the road, so you were NOT at the full mechanical advance of 22 degrees yet. BUT, since you were just cruising along, light throttle, the engine was at a high vacuum state ad was pulling the full 20 degrees advance on the vacuum advance can, so your TOTAL, the combination of the mechanical advance at "X" RPM (28 degrees using our example) added to the full 20 degrees of vacuum advance puts the engine at a TOTAL advance of 48 degrees.

Ya, but, 48 degrees TOTAL advance? My engine should be pinging like a box of marbles. NOPE. You are using light throttle, maybe on/off at times, so the engine is loafing and not under load. It'll be running lean. This high of an advance is what gives better gas mileage AND helps to cool the engine and lower coolant temps - not using a vacuum advance causes a lot of high temp woes that seemingly escape the guy trying to figure out why his engine is always running hot and he's done everything in the book with his cooling system to get temps down.

Got it? OK, so some clown in a clapped out '67 Vette with an L88 & 4-speed decides he want to run your GTO. Not one for backing down from a sure win, you drop 2 gears and nail the gas pedal. Engine vacuum drops to near zero, so the previous TOTAL advance of 48 at cruise (from above example) drops to 12 + 22 = 34 mechanical. BUT WAIT, man, you just told me above that my mechanical was 12 + 16 = 28. _YES, but at 2,400 RPM's_. Now you just dropped 2 gears in the Muncie, and put that haulin' mutha of a Pontiac engine up near 5,000 RPM's to get the jump on the whimpy L88. *Any RPM over 3,000 RPM's* (the RPM when full mechanical is reached; 12 + 22 = 34) will put the engine in its full mechanical advance point, so full mechanical has a range of 3,000 to 5,600 RPM's in this particular engine example.

OK, now you buried the L88 and he just pulled off a side street in embarrassment so you could not identify him as the driver 'cause he'd be the laughing stock at the next Corvette meet, and you back out of the gas pedal letting RPM's back down to cruise speed. As soon as you back off the gas, engine vacuum slowly begins to increase. Your mechanical advance begins to drop again once you get below 3,000 RPM's because you are slowly getting the RPM's back down to 2,400 RPM's. The vacuum advance climbs back up in the engine and pulls in the 20 degrees that is built into the advance can.

Now there _can be a slight amount of pinging _when the TOTAL advance is at its highest while cruising when at 48-52 degrees and you drop gears and pick up RPM's. Why? Because of the speed at which the vacuum is depleted from the vacuum can - the metal tube you hook the rubber vacuum line to acts like a metering valve due to its size, so the vacuum cannot exhaust out fast enough to drop the vacuum advance to near zero. So let's say you drop the 2 gears as fast as lightning, nail the gas even faster, and the engine zings right up to 5,000 RPM's in less than an L88 micro-second. Your mechanical follows suit instantaneously, because it is mechanical, and jumps right on up to 34 degrees. Well, the drop at the vacuum can is a tad bit slower, so some of that advance provided by the vacuum can is still there for just a moment. So you get 34 mechanical PLUS 8 degrees of vacuum advance that is still left by the vacuum can as it is not fully quite yet exhausted and down to near zero. So for a couple seconds, you have 34 mechanical + 8 vacuum = 42 degrees under full load. Well, you know that anything more than 34 degrees under full throttle causes your engine to ping/detonate - that's why it is set at 34 degrees mechanical. So at 42, 41, 40, 39, 38, 37, 36, & 35 degress as the vacuum exhausts from the vacuum can, you may hear a little rattling under full throttle such as when you dropped 2 gears and nailed the gas. It should only be a second or 2, and then gone - IF you experience this at all. This does not happen in all cases. There are variables in the vacuum can that can increase the vacuum drop with some being instant while some will be a little slower.

To refresh. The vacuum can *ONLY* works when engine vacuum is present. At Wide-Open-Throttle (WOT), the engine vacuum drops to near zero, so no vacuum to operate the vacuum advance. The engine uses mechanical advance only when no engine vacuum is present (WOT) and this is where the engine's distributor mechanical timing curve needs to match the engine by tailoring the springs that operate the weights that create the timing curve (plus the balancer advance).

Example #1 - Yes, as soon as you set your initial timing at the balancer, 12 degrees with the vacuum line unhooked, and then connect the vacuum line back up, it could jump to 28 degrees, 12 + 16 vacuum = 28 (my example). At idle, mechanical advance generally does not come in until around 850-900 RPM's. BUT, you can determine this using the dial-back gun. If the mechanical advance weights begins to pull an advance of 3 degrees at 850 RPM's and you need the engine to idle at 900 RPM's to run, then it would be 12initial + 16 vacuum + 3 distributor mechanical = 31 degrees at a 900 RPM. This could prove to be way too much.

Example #2 - This is where a different advance can is needed so the vacuum advance can be tailored to not only engine vacuum, but RPM, so you don't get as much vacuum advance at 900 RPM's keeping your idle advance down at the 12 + 10 + 3 = 25 - which could still be too much. You might back the Initial of 12 down to 9 + 10 + 3 = 22 degrees @ 900 RPM's.

The vacuum can has an operating range, just like your mechanical weights (timing curve) and when it has some vacuum, it only has some advance. BUT, don't get too hung up on vacuum advance and how it works, but rather, know what your engine vacuum is at idle (10, 12, 14, 16 ? etc.), how much the vacuum advance adds to the timing ( 12, 14, 16, 20 degrees of advance with full vacuum), and when added to your full mechanical advance of 34 degrees, that it does not exceed 50 degrees TOTAL when adding up mechanical + vacuum = no more than 50 degrees (although range of 48-52 can be used).

In general, with a built engine, initial timing at the balancer can be 12-15 degrees, with the vacuum advance connected bumping it up to around 21-22 degrees at idle. A stop for the vacuum advance may be needed IF you can't find a vacuum can that will do what you need to get the timing dialed in at idle and at TOTAL.


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> And yes it would be over 50 degrees if the can was 20, and that is too much. And most distributors new or old I see have that way too much timing, from both Centrifigal and vacumn.......
> 
> Put that can I said on it, hooked to full manifold. If your Centrifigal is 22 set the base at 14 BTDC, That will give you 36 Total.......with the vac can you will have 46 at light throttle cruise and 14 + 10 for 24 degrees of idle timing.....it will idle real smooth and cool there.


I got it now. I ordered a spring kit for the dizzy as well. When should I be all in by? I have to say that EVERYONE on the forums hates MSD boxes, but hearing you guys describe idle, makes me wonder why they're not worshiped.


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## Lemans guy (Oct 14, 2014)

I don”t prefer them, but don”t bash them. Racers have reasons...but on a street car with timing set correctly there is no advantage......however with timing set poorly they can cover some of the slop....just set it right and you won’t need it.


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## Lemans guy (Oct 14, 2014)

All in is a range as you have springs and weights 2600 to 3400 as a range.....3000 as the midpoint shoot for that. Also I always curve the Centrifigal to start above idle RPM.....

and don’t be afraid of 750 or 850 RPM if timing and mixture is right, often engines are modified from stock and need a bit more idle to cover the cam, the stroker kit, the big carb etc...


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> All in is a range as you have springs and weights 2600 to 3400 as a range.....3000 as the midpoint shoot for that. Also I always curve the Centrifigal to start above idle RPM.....
> 
> and don’t be afraid of 750 or 850 RPM if timing and mixture is right, often engines are modified from stock and need a bit more idle to cover the cam, the stroker kit, the big carb etc...


I have lots to experiment with, tomorrow. Will backing off the can help until the new one arrives?


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## Old Man Taylor (May 9, 2011)

Lemans guy said:


> All in is a range as you have springs and weights 2600 to 3400 as a range.....3000 as the midpoint shoot for that. Also I always curve the Centrifigal to start above idle RPM.....
> 
> and don’t be afraid of 750 or 850 RPM if timing and mixture is right, often engines are modified from stock and need a bit more idle to cover the cam, the stroker kit, the big carb etc...


There is an advantage to an MSD box on the street if you have a large cam. It gives you multiple sparks up until about 3000 
RPM, which helps clean up the very rich low RPM mode. This isn't theoretical, it's my experience.


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## PontiacJim (Dec 29, 2012)

Old Man Taylor said:


> There is an advantage to an MSD box on the street if you have a large cam. It gives you multiple sparks up until about 3000
> RPM, which helps clean up the very rich low RPM mode. This isn't theoretical, it's my experience.


My experience as well when I ran an MSD6 on an overly rich engine - made a big difference. I went with the MSD6AL for my 455 build as it has the RPM limiting feature so you don't over rev the engine and break things.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> There is an advantage to an MSD box on the street if you have a large cam. It gives you multiple sparks up until about 3000
> RPM, which helps clean up the very rich low RPM mode. This isn't theoretical, it's my experience.


PHEW! I've always wanted an MSD box, but in my younger days I couldnt afford them. Now I can, and no one will recomend one! Lol... Since I already ordered a Mallory Hyfire, I'm glad that you advocate for them.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> My experience as well when I ran an MSD6 on an overly rich engine - made a big difference. I went with the MSD6AL for my 455 build as it has the RPM limiting feature so you don't over rev the engine and break things.


Well, you two have been helping me out since day one, so I'm already sold and it's already ordered! Thanks Jim


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Well, you two have been helping me out since day one, so I'm already sold and it's already ordered! Thanks Jim


If nothing else, the over-rev protection in my book is a must as once you get those tires spinning, or miss a full blast shift, it doesn't take much to "in an instant" shoot past the safe RPM limits of the engine and do serious damage. There are other devices as well, but the MSD6AL was my pick and it's multi-spark high energy provisions that enhance the lower RPM's and can help with over rich/rich conditions - which I prefer to run versus the "lean conditions" at the "perfect" A/F ratios set for stock engines on modified engines. Too many are hung up on their aftermarket Air/Fuel guage readings. The first 2 minutes of this video notes & explains this, and I suggest you read the comments section for additional info:


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## Lemans guy (Oct 14, 2014)

This video is very good, but it really cements the reasoning to get your AFR correct.

his range, 0.86 Lamda to 0.95 Lamda equals AFR of 12.6 to 13.9.......that is the range that you want your engine operating in,.....some people try to run stoich 14.7, .....which I say and he is also saying is too lean......and richer for power, helps protect the engine and gives the desired power.....mid to low 12’s ...his 0.86 Lamda

Drivability at lower speeds is enhanced by the mid to high 13’s.....lean enough...I say 13.8 or so he went no higher than 13.9 AFR or 0.95 Lamda.

what he is saying is that people who use AFR to advocate for stoich (14.7 on pure 14.1 on 10%) or leaner are incorrect.....could not agree more, but it is not an indictment that AFR readings are wrong, in essence his whole dyno test is about AFR measured in Lamda,

and why that range is the right one for torque and power

unfortunately many tune their engine overly rich...as seen on his torque curve where it drops and overly lean.....

best to get it in the right range for power and drivability.....


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## integrity6987 (May 10, 2017)

PontiacJim said:


> The engine uses mechanical advance only when no engine vacuum is present (WOT) and this is where the engine's distributor mechanical timing curve needs to match the engine by tailoring the springs that operate the weights that create the timing curve (plus the balancer advance).


This thread has been a good read and confirms my basic understanding of what is happening with a stock set-up that I was running these past few years. Ran just like a GTO should when tuned perfectly. However, I was getting a lot of weird - less than optimum - power and pinging late in the last season. Most likely very bad fuel... I will be upgrading to a tunable HEI this year and have been studying for a couple of months on the Q-jet rebuild (Read Cliff's book a few times now plus YouTube [Harold Demes you are awesome!!] and have Cliff's kit for my carb P/N) using his recipe #2 (which after measuring some of the orifices and tubes is not too far from what was spec'd for the 7028267 (stock H.O. w/ M.T.).

From the quote above - it raises a question that maybe you can clarify with another example. My car has a 3.90:1 rear gear and I turn ~3200 RPM at 60mph. When I rebuilt my dizzy a couple of years ago I did recurve it slightly from stock. It is "all in" by 2900 and adds 20 degrees using the stock weights for dizzy P/N 1111449. The adjustable vac can I ran this last season was set to add 10 degrees with 15-17"Hg @ 2900 RPM with no load (just revving in neutral) and was reading 31 degrees. It idled great and ran cool. I don't really know what vacuum is present when steady cruising at 60 mph. I'd estimate something around 10-12" Hg. So using the above I should be at 10+ 20 mech +8ish from vac = 38. She ran awesome on 110 octane. Ran not awesome (occasional pinging) on 93 w/ octane booster. So this year will be able to easily adjust the timing and save multiple settings for whichever fuel I am running.

I hope @Machinest-guy reads this and can add some insight on the impact of modern fuels and how to compensate. Using CAM2-110 octane race gas is not a long term solution. 

I want my GOAT to smoke the L88 on pump gas.😎


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## Lemans guy (Oct 14, 2014)

Sounds like you are going to have a nice tune by paying close attention to all the details. One of the best things you can do is run a Vacumn gauge in your car. You just need rubber vac hose and don’t even need electric. Temp or permanent it will help you to dial in that adjustable vac can.

Guys make those work, you can do it you just have to pay attention and see what timing it is pulling at what vac.

each car will have different vac at 2900 RPM so the only way to know is have a vac gauge and to test the can. .....


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Sounds like you are going to have a nice tune by paying close attention to all the details. One of the best things you can do is run a Vacumn gauge in your car. You just need rubber vac hose and don’t even need electric. Temp or permanent it will help you to dial in that adjustable vac can.
> 
> Guys make those work, you can do it you just have to pay attention and see what timing it is pulling at what vac.
> 
> each car will have different vac at 2900 RPM so the only way to know is have a vac gauge and to test the can. .....


UPDATE:
Installed a Crane Vacuum Reserve and and Autometer vacuum gauge, that I had new in the box

I found a vacuum chart for the dizzy can and I attempted to adjust it. It specified that at 10hg that I shouldve gotten 16-17 degrees of timing, but with the base at 12 degrees and the can connected, I got 22.

As usual, the car starts and idles like a dream, and when put in gear, it was DEFINITELY acceptable. You can drive it around and it's not fun, because it BARELY stays running at a stop, and if you do a hard stop, it's dead before you're done rolling. SO!!!!!!!!

As before, it ONLY dies after a hard stop. Is there a way to test the torque converter? I really want to convert this car to a manual trans, so the last thing that I want to do is drop $500 on a converter install, which I don't need. Any converter recommendations, based on my cam? Does it look like this cam would be giving TC issues with a stock TC?

I'm optimistic that the new vac advance can will help a lot, but if the car is ONLY stalling after hard deceleration, then something else is wrong.


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## Lemans guy (Oct 14, 2014)

I use a Coan Racing Torque converter,.2400 to 2600 stall. I have been to their plant in KoKomo Indiana, they make em, and sell direct, but JEGS, Summit carry their stuff as well. But will be near $500. They have any stall you want for TH350 or TH400.

22 degrees BTDC at idle is good and with 10 degrees from vac is what you want, that new vac can will provide that as well.

you can talk to Coan direct, they are helpful. Also Performance Torque Converter (PTC) in Muscle Shoals, Alabama is very good builds their converters on site, been there too easy to talk to and work with. Usually good prices.


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## Lemans guy (Oct 14, 2014)

Maybe it is the converter, ....

as you drive and the throttle is still mostly closed, light throttle, you vac increases and so does your RPM......the vac goes from 10 to 15 HG........with that adjustable vac can......it may pull more timing as vac increases......maybe too much....

......you can watch your vac gauge and see what your vac is at various RPM’s.

That fixed can is better,....only will pull 10degrees, and will pull it below your Idle vac of 10 Hg.


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## armyadarkness (Dec 7, 2020)

So, as I understand timing more, now I get why they made recurve kits. My dizzy is a Proform HEI and I called them and asked, can I limit my mechanical advance? They said "yes", with a bushing kit. However, I looked everywhere for the kits and I dont see them. Some say that the weights do the limiting, some say the springs do it, others say that it's bushings. Which is it? 

Right now it's fixed at 22. An MSD Pro Billet is about $500, so if I can limit this one, I should.


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## Old Man Taylor (May 9, 2011)

My Pro Billet does not have the capability of having vacuum advance.
The bushings reduce the total advance. The springs and weights determine how long it takes to get to the total advance.


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## armyadarkness (Dec 7, 2020)

I just got off the phone with the cam company (again). They said that there's no way this car would idle in gear, with the stock converter, and that it would prefer 3.73's. So, good info, but I take it with a grain of salt, since those gears seem too much for a Pontiac. He said my timing should be all in by 1200 and that the converter needs to be at least 2400


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## Old Man Taylor (May 9, 2011)

I would never talk to that guy again. First the gears have no bearing on the idle performance. Second he’s giving you recommendations for a race engine. You would like your advance to be all in at 2500-3000 RPM. Third you want a converter that matches your needs for street performance. In this case His recommendation might be OK depending on what you want.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> My Pro Billet does not have the capability of having vacuum advance.
> The bushings reduce the total advance. The springs and weights determine how long it takes to get to the total advance.


The one I looked at, did have vac adv. I was always told that bushings limit... but after two days of searching endlessly, I found no limiting bushing kit for an HEI, and when I looked at 10 different recurve kits, none mention bushings for limiting... They only mention bushings for the weights. Yet... Proform insists that my dizzy will accept limiting bushings.

Man... MSD, Holley, Mallory, Mr Gasket... none of them have any mention of this with their kits. It's not like I'm trying to view the map for buried treasure. I don't see why it all has to be so hidden. Once again, all of the information is at our fingertips, and yet somehow, the internet makes it harder to find.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> I would never talk to that guy again. First the gears have no bearing on the idle performance. Second he’s giving you recommendations for a race engine. You would like your advance to be all in at 2500-3000 RPM. Third you want a converter that matches your needs for street performance. In this case His recommendation might be OK depending on what you want.


Yeah. He mentioned that the torque wouldnt be where I wanted it, without those gears. And my thought was, we're talking about a Pontiac... what am I missing?


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## Old Man Taylor (May 9, 2011)

Sorry, I was referring to a standard distributor, not an HEI. Mine is on my race car, so I don’t care.


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## Lemans guy (Oct 14, 2014)

So a typical HEI curve kit has different weights in it. Those weights have a slightly different shape and therefore limit the Centrifigal,advance by putting them on. Many will give you 18 degrees. So yes some dizzy’s have bushings like some MSD, but other MSD dizzy’s just use a standard HEI curve kit and swap the weights in the curve kit.

Moroso curve kit for HEI is part #72300.....for GM HEI......don’t get the 72310 that is for GM Points dizzy. It has springs in it as well.

but look you already have 22 Centrifigal, that will run great, I would set that at 14 base giving 36 total...base 10 + Centrifigal 22 degrees....=36.......now add the vac can I told you about and your idle timing will be 14 base and 10 from vac for 24 degrees it will idle cool and smooth there.

now you can try various springs like start with 2 medium from the curve kit or a light and a medium and test drive. You can mix the springs. Listen for pinging and detonation, if you have any dial the base back2 degrees to 12 and retest.....still there retard 2 more.

Most cars can take 36, I know PJ likes 34 and that is good as well, a little more conservative. Either way you have to test for pinging.

If you an extremely radical cam you can add more idle timing. I have set lot’s of dizzy’s up at 18 base and 18 centrifigal for 36.....I only add 10 from vac cause that is the max you want on today’s gas.....and then idle will be 28 degrees....radical cam take it, yours might.

But going from 18 to 22 Centrifigal is not all that much different as as soon as your RPM’s go up that 4 degrees comes in anyway......


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## Lemans guy (Oct 14, 2014)

Oh and agree with Mr. Taylor that that counter man advice on all in at 1200 is dumb, your idle my be 800....400 RPM will come in at first touch of the pedal at a stoplight...this will mess your engine up for sure....it is a range you get from the springs...

2600 to 34 say....shoot for 3000 anywhere close and you are good try not to add Centrifigal at idle, springs that are too week will do that....not sure how that counterman can make spr
ings go from 800 all in by 1200, he must be making those springs in his own factory or using rubber bands.....

Listen to PJ and Mr. Taylor and Bear they know. Also Race cars are different they are doing things to win and add speed, not everything racers do you should do.


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## Lemans guy (Oct 14, 2014)

Ps on the curve kits...preform sells one for GM HEI.......the weights and center cam change the Centrifigal advance on these style HEI

What the counter man is mixing up is the curve kit for a non HEI or points style GM distributor. Those come with limiter bushings. Small brass bushings that limit advance of the weights.

Some after market MSD have a system like that but they are manufacturer specific.Yours probably just takes the GM HEI curve kit MORoso or preform will fit. About $6 to $10...

really you just need the springs. 22 is good. Too much timing at idle can kick back the starter and make for hard starting.


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## Lemans guy (Oct 14, 2014)

Points dizzy’s and HEI differ on not only internals but the diameter of the dist body, the HEI is wider......the “Points” style is narrower, vac cans are not the same lengths.....setting the limit of the weights is done with bushings on points and generally weights and center cam on HEI

unless Mfg specific system like MSD


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## Lemans guy (Oct 14, 2014)

You want vac advance on a street car...it gives idle cooling, smooth light throttle with lots of power, by adding 10 degrees of timing...and does not hurt your top end because it drops out when you floor it....no vac..no vac advance timing......

don’t let a counter man talk yo7 out of vac advance......when set right it is a tremendous improvement in your overall operation


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> So a typical HEI curve kit has different weights in it. Those weights have a slightly different shape and therefore limit the Centrifigal,advance by putting them on. Many will give you 18 degrees. So yes some dizzy’s have bushings like some MSD, but other MSD dizzy’s just use a standard HEI curve kit and swap the weights in the curve kit.
> 
> Moroso curve kit for HEI is part #72300.....for GM HEI......don’t get the 72310 that is for GM Points dizzy. It has springs in it as well.
> 
> ...


My fear is that "I think" I am pinging at 36. I don't know, because I don't know what pinging sounds like. But, when in 3rd gear, if I nail it and it doesn't down shift, THEN (only) it sounds rattly, like the valves are floating. Is that pinging? I think it might be, because its intermittent, so I assumed that it was related to my constant tinkering with the ignition and timing.

The 22 at the dizzy seemed a bit high, if I needed to boost my initial, but a lot of this is speculation at this point. Here are the facts:

I did order the can that you recommended and it'll be here Thursday.
At least once, I suspect that I set the timing wrong (I think I used the 6 mark, not the zero), so my pinging, if it was pinging, couldve been then.
There are literally about 20 recurve kits, now, thanks to amazon. And none seem to have instructions. So, I'm really trying to not buy ANOTHER dizzy for $500 (which will make it about $900 that I've spent on dizzy's for this car, this month) but I also don't feel like ordering $20 kits, every other day, until the law of averages gets me the right one. Heck, I'm not even comfortable owning a distributor, where the manufacturer cant give me a part number for a kit... nor am I comfortable buying kits, when the manufacturers can't tell you what they fit of how they work.
When the snow and salt are gone from the road, I will disconnect the vac can, advance the base to 20 and see if it helps idle in gear. If so, then at leat I know that timing is my issue and not the torq converter or a vacuum leak.
If the timing is the culprit, and the can that you recommended fixes it, then great, but I wanted to at least have all of the recurve parts, on hand, in advance, so that if I need to increase the base, I can, without having to wait another week for a $20 part.
I also do have a Mallory ignition box coming, so that will replace the Proform dizzy module. And if there is a God, then between that and the new can, after 2 months, this car will actually drive!


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Ps on the curve kits...preform sells one for GM HEI.......the weights and center cam change the Centrifigal advance on these style HEI
> 
> What the counter man is mixing up is the curve kit for a non HEI or points style GM distributor. Those come with limiter bushings. Small brass bushings that limit advance of the weights.
> 
> ...


I looked at at least 10 kits, and none of them had more than one set of weights, but as I mentioned, some people said that they limited max mechanical, and other claimed that they didn't change the mechanical advance, they only changed the rate at which it hit. Proform insisted that it's done by a bushing under the weights. I ordered the Moroso kit that you suggested, and it claims to fit "All GM HEI". Time will tell.

In any event, that kit will just be, Plan B. I'm pretty sure that I'm already set to 36, all in at 3000, so hopefully, just adding your can will do it.

Then my biggest decision will be, do I put a $600 torque converter, into a car that I want to make a manual?


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> You want vac advance on a street car...it gives idle cooling, smooth light throttle with lots of power, by adding 10 degrees of timing...and does not hurt your top end because it drops out when you floor it....no vac..no vac advance timing......
> 
> don’t let a counter man talk yo7 out of vac advance......when set right it is a tremendous improvement in your overall operation


I just hope that I have the vacuum to pull it. I barely have 10, when in gear.


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## Lemans guy (Oct 14, 2014)

That is a good plan, that vac can will pull all ten degrees under your 10 Hg at idle. The specs start at 3 Hg all in by 7 to 9 Hg. Easy to check once you set your base with vac disconnected and plugged, don’t forget the plugged part......the. Just connect the can and it will and 10 degrees timing.

Yes agree I think you had way too much timing and that will cause pinging, You are getting closer did you richer your idle mixture? You still may be too lean.

You can tell when your carb moves from idle mixture to main jets by watching the boosters as you run the throttle with your hand.

In park, brake on, wheels chocked, preferably a helper, remove air cleaner and watching a tach run the throttle up and note the RPM when the boosters come on.......everything below that RPM the car only runs on the idle circuit, when you are stalling, it is on the idle circuit.......


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## Lemans guy (Oct 14, 2014)

Main jets come on near 2500 RPM, every car a bit different....but good to know.


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> That is a good plan, that vac can will pull all ten degrees under your 10 Hg at idle. The specs start at 3 Hg all in by 7 to 9 Hg. Easy to check once you set your base with vac disconnected and plugged, don’t forget the plugged part......the. Just connect the can and it will and 10 degrees timing.
> 
> Yes agree I think you had way too much timing and that will cause pinging, You are getting closer did you richer your idle mixture? You still may be too lean.
> 
> ...


When I'm stalling, I'm not giving it gas at all. It's when I let off the gas and hit the brakes, that I stall. The engine die before the car stops rolling. Yes I did richen the mixtures dramatically. Then I test drove it and it made no difference. Then, I took a screw driver, hit the road, tested it and noted that right when it died, the AFR went down into the low 11's. So I leaned it a bit, and no difference, then I leaned it more, no difference, then I leaned it a lot more and it came up, but not much. After making a full turn in lean, it was still in the 12 to low 13's, and/ or 11's when it began to die. So...

Can we assume that I'm not burning the mixture when it dies?


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## O52 (Jan 27, 2019)

There is a Distributor Guru by the name of David Ray. Dave is a crusty old guy who was an engineer at Delco and who helped design the HEI distributor. A lot of people don't like Dave but I have found his advice to be solid when rebuilding my distributors. He will gladly talk to anyone regarding timing problems and in my case it was over an hour and a half. 

He has a service to convert small (points) distributors to HEI. Unfortunately he is still recovering from a venomous spider bite that prevents him from working with his hand.

With all that being said he has a website that has a lot of good information regarding timing, specifically vacuum canisters and how to adjust them. There are also notes regarding coils and distributor gears as well as his conversion service.

Read all his notes at the bottom of the page. 






DAVE's small-body HEI's


Conversion service for HEI Electronic Ignition Systems for Point Type Automotive Distributors




www.davessmallbodyheis.com


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## armyadarkness (Dec 7, 2020)

Wow. Lots of information there! I have a lot of experimenting to do when the weather clears.

I talked to the engine builder today, finally, and he confirmed that he didnt change the converter and that it would be far too tight for that cam. Great news, but... why did he leave it then?


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## Lemans guy (Oct 14, 2014)

Sounds like the answer....as the throttle drops on deceleration the tight converter stalls the engine by not letting the flywheel turn, that also would cause the cam and therefore the distributor rotor not to spin....the whole firing train is interrupted,...no spark.....and consistent with a rich AFR reading and a stall.....maybe....

still need the timing right, but it may not stop that stall, ...looking like your converter.

Like you say if the builder knew it would not work why proceed......


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## Lemans guy (Oct 14, 2014)

Misfires really show as lean....because the mixture is unburned and therefore has more Oxygen in it....and that shows as lean normally....

an overly rich condition could be caused by a few things, like too high float settings, too much fuel pressure, a leaky power valve or accelerator pump,......but I think you have worked those things already

So you are back to the converter......your choke flap is not moving to a closed position is it? That could make it rich.......

also too little air can make it rich....like a too small air cleaner or blocked air cleaner.....


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Wow. Lots of information there! I have a lot of experimenting to do when the weather clears.
> 
> I talked to the engine builder today, finally, and he confirmed that he didnt change the converter and that it would be far too tight for that cam. Great news, but... why did he leave it then?



If you would stop overthinking every move and listen for a moment to our suggestions, you'll be ahead of the game and minimize the grey hairs.

I believe I already made mention of the need for a higher stall converter, no? Would you keep the clutch locked up at 750 RPM in 4th gear coming to a stop? The car would be bucking all over and maybe even pop a u-joint, but I guarantee it'll stall out. This is why cam manufacturer's recommend a higher stall converter and even lower gear ratio's, as well as needed compression ratio's specific to the cam selection.

Throw the A/F meter away - they are more confusing than good. They are like a mirror, do you keep your eyes glued to the mirror when you drive? No, once in a while you glance in it, but you don't drive by it. Old school seat of the pants is best. If running pump gas, read the label, may contain up to 10% ethanol. How do you know you don't have 2% today and 10% the next fill up? What if you get a slug of water, or the ethanol has settled out of the gas in your tank because it sat? What if you add octane boost or racing gas? I think this gauge does more harm than good because you can not look at it and oops, what did that number just mean and why did it just spike up, or down, must have an issue that I gotta look into and adjust out. And, to really be accurate, you should invest in a 5-gas exhaust analyzer.

Read this article carefully, pay attention to the results of a bigger cam, and lowered fuel vaporization. Lot of good info.

Carburetor Tuning: A/F Mixture, Air/Fuel Equation - MRK Motorsports Official Site 

*Lemans guy* has provided all the needed info with regards to timing and distributor settings - this is what he does, and his advice is through experience and once you follow his guidelines and then you experience any deviations, he will guide you through that as well.

So, your options are to purchase a higher stall converter or accept the stalling issues and wait until you are ready to purchase the manual trans. Throw the trans into Neutral whenever you are coming to a stop, or near stop - this can work temporarily until you get your manual trans swap in place.

Select a distributor, HEI, points, electronic conversion, aftermarket or stock set-up and then work with it, period. I personally don't like factory HEI's as they have a few features not useful, in my opinion, for any real high-performance use without modifications - and they are old and parts hard to get.

Dave Ray has been on the forum here and you may find his babble. I will only say, my opinion, I don't care for the man or his stuff, but others swear by it.

Going to a points distributor will work just fine - did just fine for the factory and they some even had factory dual points for their high-performance engines. The short comings are they have no vacuum advance. Did you know the factory 1956 Pontiac 285HP 316CI optional "Nascar" engine used a factory dual point distributor? Points only get a bad wrap because the art of setting them up has been lost and the HEI/electronics types are essentially install and run.

Aftermarket distributors come in different options. Ask which is the best, and its like asking what the best cam is. The only way to really know is to do a little research and pull the trigger and go for it. I always look at the dates when "negative" reviews are posted. Often they are 10-15 years ago. The manufacturers listen, make changes to improve, and now you get a rather good product without issue. Just make sure it has the adjustability you want out of it. If unsure, email the manufacturer - and yest, some reply will come from some guy who knows nothing because he is reading off the Cliff Notes for the product, especially when emailing someone who is a middle man and not the actual manufacturer.

Here are a couple new entries into the Pontiac field by Speedmaster. I read they are an Australian company, but the PY guys say parts are from China - isn't everything? They have 2 offerings. There is one called the "Rayo" and may even be associated with Dave Ray? 

https://speedmaster79.com/ignition-electrical/ignition-components/distributors?enginemake=Pontiac 









Pontiac 326 400 455 6000 Series 65K Coil HEI Distributor [Red]


SpecsBrand:PCEPart Number:PCE376.1053Part Type:DistributorsProduct Line:6000 SeriesComputer-Controlled Compatible:NoTrigger Style:Magnetic Advance Type:Vacuum and mechanicalCap Style:Male/HEIMechanical Tach Drive:NoSlip Collar:NoGear Material:SteelIgnition Box Required:NoDistributor Gear...




speedmaster79.com













Pontiac 326 400 455 - El Rayo DNA® - Distributor Ignition Kit


SpecsBrand:SpeedmasterPart Number:1-385-008Part Type:Ignition System Combo KitsProduct Line:El Rayo Advance Type:MechanicalIgnition Box Included:NoRev Limiter:NoIgnition Coil Included:YesCoil Style:E-coreDistributor Included:YesWiring Harness Included:YesSpark Plug Wires Included:NoSpark Plugs...




speedmaster79.com





I like Pertronix, but they are not inexpensive. Some hate them. Had no issues with the Pertronix electronic conversion with my stock distributor, others had problems, but that was years ago and Pertronix has improved the units so as to protect them from burning out. Installed a Pertronix conversion in my brother's 1948 International flathead 6. They make them for just about any vehicle and if they were that bad, they would not be selling.

So the bottom line is to listen, and just do. Too much research, too many opinions, too many choices, too many reviews, and worrying about the best price or not, and you might as well just put your car into a shop and let them do the work and when it is not right, you can chew them out and get them to correct it.

Just my opinion.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> If you would stop overthinking every move and listen for a moment to our suggestions, you'll be ahead of the game and minimize the grey hairs.
> 
> I believe I already made mention of the need for a higher stall converter, no? Would you keep the clutch locked up at 750 RPM in 4th gear coming to a stop? The car would be bucking all over and maybe even pop a u-joint, but I guarantee it'll stall out. This is why cam manufacturer's recommend a higher stall converter and even lower gear ratio's, as well as needed compression ratio's specific to the cam selection.
> 
> ...


I'm definitely hearing and heeding everyone's advice, and waiting on parts at this point. Yes, you did mention the stall converter, early on, and since I had never gotten into converters before, nor did I know the history of mine, I did my due diligence.

Yes, I did install a Mallory dual point on my 66 GTO, back in the late 80's, so I'm very familiar with them.

As for overthinking stuff... Some people smell, some people are selfish, and some people have OCD. At 52, I probably won't be changing soon, but if I have to have a poor quality, I'll take the one that gets me paid! Yes, I am "too" detail oriented and it's a double edged sword. It's annoying to me, but it's also why I'm the best at what I do.

As I've mentioned I'm an investigator for the government, and one of my primary, daily functions is to inspect fuel and certify the octane. But, I don't live by my AFR, I use the gauge to tune carbs and diagnose issues.

Your knowledge isnt wasted on me, Jim. Although I may process it it in an unorthodox way. Either way, thanks for the help.


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> I'm definitely hearing and heeding everyone's advice, and waiting on parts at this point. Yes, you did mention the stall converter, early on, and since I had never gotten into converters before, nor did I know the history of mine, I did my due diligence.
> 
> Yes, I did install a Mallory dual point on my 66 GTO, back in the late 80's, so I'm very familiar with them.
> 
> ...


I understand the OCD, but set down on paper a "plan" of action so as to focus. Keep it as a guidebook of sorts. If you have a question or offshoot within the main topic, or plan, then make a note off to the side next to the main topic and then throw it out here if it needs sorting. DON'T keep it all in your head, set it in front of you so you can see it and add/subtract from it as needed.

You want to dial in one aspect of your car at a time as too many adjustments can cause the problems you are having and you are simply chasing your own tail. Don't assume all your adjustments are done and the results didn't quite get you where you wanted to be and then move on to the next thing that you think will fix or help. Write up a list of the adjustments & changes you make, then what your results were, and if you kept the change, or reversed the change and moved on to another adjustment.

If you post these kinds of things, adjustments/changes and the results, many on the forum can then analyze what you are doing, or not doing, and guide you much better.

A bigger than stock cam can produce a number of results to the engine, whether simple idle quality, or running in general. What carb, ignition, and or other components is almost irrelevant in choice, but is relevant in its dialing in and adjustments. Keep in mind the engine is a dinosaur and has to be looked at and adjusted as such.

So make your adjustments "old school." Adjust your carb so the engine runs its best "by ear." Don't go adjusting for best vacuum right now. Turn 1 idle screw in until the engine runs rough. Back it out until it raises RPM slightly and runs smooth. Then turn back in until it runs rough again. Then back it out one more time until it runs smooth again - you're done. Do the other the same way. Then set your idle speed to where the engine sound lopey, but not too low its going to stall. Follow a little of the AVS2 adjustments from the manual. You may have to change the power valve spring to match the engine's vacuum, or My guess is between 750-850 in Neutral.

When you drop it in gear, it is most likely going to dive and run rough because the idle is too low. BUT, if you raise the idle so it runs smooth again, my guess is that's when the engine RPM's want to override the factory stall speed and you have to either keep your foot firmly on the brake to keep the car from wanting to take off on you, or a combination of footing the gas pedal to keep RPM's and engine vacuum up AND an even heavier foot on the brake pedal to keep it from rolling forward and stalling out.

You could try an aftermarket vacuum pump to help increase vacuum IF you think that may help. Many modern cars use a 12-Volt vacuum pump to operate the brakes. If you do a google search, Amazon seemed to have a number of them for cheap. You don't have to go on Summit or Jegs and buy a high dollar unit.

Again, throw the trans in neutral when coming to a stop may be a temp fix for now. Have you tried this? It should allow your engine to maintain its idle RPM ad keep vacuum up to operate the brakes and not stall out. If it is still stalling out, then I would say it may not be the low vacuum due to the cam, but a vacuum leak within the engine's system - to include the "new" brake booster and check valve going into the booster.

In any case, once you get the carb adjusted and the engine running/sounding smooth, tackle your timing and timing curve to coincide with the smooth running of the engine (whatever distributor set-up you use). Use *Lemans guy*'s suggested timing & timing curves along with the recommended vacuum can and its settings. Once you get this adjusted, now take it for a drive and see how it feels in the seat of your pants - old school style. Listen for any "pinging" or detonation and if any, then back you can either back down the timing a few degrees, add a limiting stop to keep the distributor timing from over advancing, OR stretch the RPM's up higher to around 3,500 RPM's as to when full mechanical timing comes in - and you can do a combination of all of these as well.

You may also need to go back and re-adjust the carb again after getting you timing right. Sometimes you may find that advancing the timing causes the idle to speed up, or retarding it may cause idle speeds to drop, and now you have to re-set/fine tune your carb idle and/or mixtures to match.

Get this dialed in, you now have the carb set, the timing set, and can now determine if you still have the same issues with stalling when braking to a stop. If so, then I am inclined to say a looser converter may be the answer.

Once you have things set "old school" then you can go back and adjust for best vacuum or best A/F ratio based on a known set-up that works. If you make any of these adjustments and the engine seems to go a little south on you, then you know to reverse what you did and keep it there regardless of what the gauges tell you.

Each car/build is different and I am not saying I have all the answers. Others here also provide great advice. My suggestions may or may not be the answer, BUT, it is how I would tackle the symptoms you are describing and encountering. I have never used or read much on the 4/7 swap cams and don't know if this in itself can pose a problem as you are having, so what I am suggesting may be steering you down the wrong path, I don't know to be honest. I just know that you want to work with adjusting each item on the car that could be the contributing factor to your symptoms and thoroughly make every adjustment I could to rule out what it may be, or what it may not be. Then move on the the next part that can be adjusted in an attempt to get the car running as it should.

So for me, it would be carb, vacuum check, ignition, and converter.


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## Lemans guy (Oct 14, 2014)

Well said PJ, really these cars and all hot rods need a holistic approach. When someone says their car runs rough, that is important info. Even if any kind of meter says it is good.

experience, yours matters, and you army are an old car guy. So like PJ says seat of the pants matters, how the idle feels to you matters, how you think it smells matters, how it drives, and what meters say, Vacumn, RPM, AFR, timing light, 5-Gas, fuel pressure on and on.

I have no doubt that you will get it running cool and smooth whatever it takes.


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## Machinest-guy (Jul 19, 2019)

Good morning integrity6987 , I read your email request that I dive in with some opinions. So I read the prior remarks more or less completely. I would add only some general observations. Then a bit of insight about some of my current projects.

We are at a time in tuning history where conventional mechanical timing and carburetor fuel devices are no longer adequate to achieve the results we want. This is because of fuels chemical differences from when our historic cars were engineered, and day to day variations in fuel quality and composition. There is also an expectation factor which is outside of this conversation, yet it should be acknowledged. Hence we can only really set up an optimum tuning combination within a limited window, perhaps for a specific day or run, with mechanical components. Or we can accept less than optimal performance. Or we can move our older ignition systems technology ahead in time to more modern methods of timing and fuel control. 

Mechanical timing and fuel delivery systems were designed only with response to speed, load, and air velocity. Modern fuel, to be burnt effectively, needs control over air density, temperature, quality, and other dynamic factors, in addition to load and speed. The same can be said for timing controls. Modern engine control systems do this electronically in ways mechanical devices cannot. So to burn modern fuel acceptably well updating a gravity dependent, acceleration error prone carburetor and speed sensitive distributor with electronic sensors and controls is nearly mandatory. Here are two products which can further that goal.

MSD Ignition 8680: Adjustable Timing Control For use with MSD Ignition Controls | JEGS and 




__





Universal SafeGuard for Distributor Ignition






www.jandssafeguard.com





A few years ago I was having dinner with Rick Gold, owner of ERC racing fuel, after he made a presentation on fuel technology. We discussed timing controls for high performance cars among other issues. He made an interesting comment in relation to GM products. He said if modern GM engines didn't have knock control GM would lose more than half of their production to detonation failure. In his research he'd found 100% of the vehicles tested were running under some degree of timing retard because of inadequate fuel. This was in the 1990's when MTBE was introduced.

He also made an interesting comment that modern "gasoline" was by volume 50% additives which composition changed according to which company the fuel was blended for and when. And every blend needed a different "tune". 

The old homily of "we have been doing so much for so long with so little" comes to mind when I consider how to tune an older vehicle. Particularly one which needs to present itself as "stock". It is hard to do when modified, doesn't stay done when used, and might require a different process to do again. 

I guess we could get into why jet sizes I use at sea level won't be right for fellows in the Midwest or mountains. I guess we could parsec ignition advance curves vs. ambient air temperature and under hood heat too. And maybe investigate the effects of initial ignition timing vs. camshaft timing for hours in terms of distributor weights, springs and brake mean compression pressures. I'd just offer up what I see here isn't what you have to deal with there. So it is how we find solutions and how those translate into hardware that matter. 

While I'm working on my GTO to upgrade the engine with an OEM tri power and ram air system, I'll likely update my ignition system to an MSD and spark knock control box. It is just going to be easier to deal with. My tune up plan is to set about 15 degrees initial timing at the crank and let the control box retard that if it doesn't start easy. I'll put about 45 degrees advance into the mechanical and vacuum advance controls and let the spark box cut that back as needed dependent on what it's temp and knock sensors tell it to do, at a whole lot faster adjustment rate than I could ever could do manually. Every moment of every drive I'll get a different tune to suit the conditions present at that moment. Very nice.

Once the ignition is working I'll set jetting by using an A/F gauge that can log over time then average those measurements.The whole argument of setting up to run a bit lean or rich I understand from flying a piston aircraft with engine fuel and exhaust temp monitoring. Basically; rich runs cooler at the valves and hotter in the pipes. It fouls plugs but is safer from a stall than being lean. Running lean gives a bit hotter cylinder temperature, a bit lower exhaust temperature, and better economy with penalty of reduced power output. All of that translates directly to automotive engines in cars. 

Currently I'm working on a vintage Ford GT40 fitted with an all new all aluminum 427 SVO dry sump engine. It is set up with 4 twin venturi Weber IDF carburetors on a custom manifold with a dual (RH & LH) pump and fuel rail system. It has clear 3D printed carb spacers so we can see the mixture atomization. And it has thermal barrier air box and protected fuel system components. The car owner and I designed and then made all these components over the last two years following to some degree photographs of how the cars were set up for the Le Mans races in 1967.










The things I did to make this engine run on modern fuel are the same as what needs to happen on our Pontiac's. They are thermal control of heat getting into the carb(s). Some assurance (visual) of atomization taking place and then correcting (minimizing) droplets running down the manifold walls. Air flow control with an air box or contoured air cleaner base. Strong ignition spark. They are the same on this large engine as a small one I built for a Mini Couper owner for the 2017 Canadian / American Challenge race. We won stock class outright and beat many modified class cars by paying attention to re-engineering tuning fundamentals of thermal dynamics and physics of combustion into the hardware before tying to somehow adjust old fashioned parts to run on modern fuel. A big help for the Mini Cooper came from thermal barrier coatings. They would help a Pontiac engine a great deal also. In the Cooper project I had the head fully coated in the combustion chambers and ports. I wanted to limit heat from the head getting into the intake mixture and limit heat from the exhaust from getting into the head at all. I wanted to hold heat in the combustion chamber to expand the gasses in there to make power, then blow remaining exhaust heat clear out the back as thrust. 











The Ford engine pulled 510 HP at 5000 RPM on the Ford dyno with a single 4bbl and shorty dyno headers. With the Weber carbs and correct tuned headers it should come in at 560ish with 427 cid. That is 1.3 hp / cubic inch. The Mini engine pulled 97 Hp at 5000 RPM from 1300cc (80 cid). That is 1.2 hp / cubic inch on twin bone stock Solex carbs. Our Pontiac engines make about 360ish horsepower from 389 -395 cid or .9 Hp / cubic inch. That calc shows me picking up more power is possible with parts now available for Pontiac engines if the thermal dynamics of the hardware are correct. Then comes correct tuning. The Mini Cooper actually did much better on the track because my engine was designed to run between 5000 and 9000 RPM. The dyno operator feared a failure of his wheel driven dyno if run above 5000 RPM so cut us off just when the engine was starting to pull. This illustrates another point. Tuning in the Pits or garage isn't the same as tuning on the track or street. The Mini Cooper's cold air induction and ram air air box were not at all functional on the wheel dyno. That same thing is true for Pontiac vehicles. Baseline tuning specifications when running old parts with new fuel are guidelines, not fixed facts.

I hope this rambling sets you on a path towards a successful tune up. These days the hardware needs an upgrade before the fuel will work right. Best to all. Ladd


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## Lemans guy (Oct 14, 2014)

Thanks Machinist guy, that is some super cool assessment. Looks like you are dragging every inch of HP out of both of those engines.

The fuels are so different now that it really takes paying attention to all the factors that you can to make it as best you can and want for your driving habits and desires and conditions.

one question, wouldn’t a hotter intake manifold reduce intake wall wetting, as as the fuel moves from carb to the intake it vaporizes faster.....

or would it be better to have a colder intake manifold........

of course there is then the question of which is better for raw speed and which is better for drive ability...

I do believe that paying attention to heat matters and I wrap my fuel lines in heat wrap, use phenolic spacers, and jet coated QFT carb all to reduce heat.....and heat soak after shutdown...

Thanks for all of this great info


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## Machinest-guy (Jul 19, 2019)

Lemans guy said:


> Thanks Machinist guy, that is some super cool assessment. Looks like you are dragging every inch of HP out of both of those engines.
> I appreciate your complement. The Mini project was a few years in development and made a good story which was edited then published in "Engine Builder" magazine. It won me a nomination for engine builder of the year which didn't go anywhere but it was nice to be nominated. Someday I'll post it to my website.
> 
> The rules for that class specified "visually period correct appearance, no roller rocker arms, no titanium valve retainers". And I had to use stock unmodified Solex carbs. So my design immediately became very aggressive thereafter internally, and with the chassis.
> ...


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## Lemans guy (Oct 14, 2014)

One last question.....exhaust crossover port on intake under carb,.....makes cold drive ability much easier..........does it rob power? Have blocked them and opened them.....this is for street cars.......just seems a smoother easier drive with it open.....but it may lose some HP....maybe just on higher end......your thoughts.....and thanks

I know the gang appreciates you taking a few minutes to share this with us...


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## Machinest-guy (Jul 19, 2019)

Lemans guy said:


> One last question.....exhaust crossover port on intake under carb,.....makes cold drive ability much easier..........does it rob power? Have blocked them and opened them.....this is for street cars.......just seems a smoother easier drive with it open.....but it may lose some HP....maybe just on higher end......your thoughts.....and thanks
> 
> I know the gang appreciates you taking a few minutes to share this with us...


This is deceptively complex. I'll have to write tonight or tomorrow. Cutting a hole in my hood now and want to finish. Ladd


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## Lemans guy (Oct 14, 2014)

Understand!......thanks


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## Old Man Taylor (May 9, 2011)

Lemans guy said:


> One last question.....exhaust crossover port on intake under carb,.....makes cold drive ability much easier..........does it rob power? Have blocked them and opened them.....this is for street cars.......just seems a smoother easier drive with it open.....but it may lose some HP....maybe just on higher end......your thoughts.....and thanks
> 
> I know the gang appreciates you taking a few minutes to share this with us...


Impact to street performance will be fairly negligible, especially if you don’t tune the engine around the blocked crossover.


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## Machinest-guy (Jul 19, 2019)

Ok, here goes. Heat crossover. Lots of opinions where there should be agreement. Forgive me if I sound like a service manual because how this works comes right out of any GM service manual for carbureted series cars. The heat crossover is part of the carburetor choke system and works in conjunction with the heat riser valve mounted in one of the head pipes. 

Next, a story to make this interesting, then we'll go back to the textbook. 

In the early 70's a buddy was building a road race Corvette with SBC power. Somehow he messed up his intake gasket block off adapters and didn't have any others handy but he did have a furnace and forge...... so we melted some junk pistons and filled the intake manifold crossover full of aluminum which plugged it solid. We also filled the head section too. Job done; but we wondered if we'd also messed anything up because we didn't really understand what we were doing in regard to how that change effected engine operation. So we read the manual to figure it out. 

When an engine cold starts the choke is typically shut. Low air flow and low pressure at the venturi create a puddle of liquid fuel in the intake manifold as the carb tries to deliver something to the cylinders that will ignite. This is very bad for fuel economy and very bad for engine upper cylinder lubrication so this pig rich system condition needs to do it's job and then get shut down as quick as possible. A heating crossover passageway is the solution for liquid fuel puddles. When the engine starts hot exhaust gasses flow out of the ports and into the head pipes equally. The exhaust crossover is a balance tube between the banks with potential to deliver heat energy if there is some means to upset the balance of exhaust pressure to create flowing hot exhaust in the passageway. The heat riser valve is also shut on cold starts which creates more back pressure on one side than the other so hot exhaust gasses flow through that passageway which brings the intake manifold above the vaporization temperature of gasoline which creates a vapor the engine will run better on as it warms up. 

Another story. This is the moment, if you were an owner of a high end Packard or Cadillac running updraft Stromberg carburetors, you'd get out of the car and open the side bonnet to open an intake manifold drain valve which would allow unused gasoline to drain onto the ground and get it out of the intake system. Then you could accelerate the engine.

So as your Pontiac warms up and the "Cold Engine" light goes out - remember those ? you can accelerate the engine with greater throttle opening. The choke is open, the heat riser is open, there is no back pressure differential so those systems are ineffective until the engine is shut off and cools off. Hence you notice nothing happening because when those systems were active the choke was the biggest air flow limiting factor and the engine didn't make any power because it was shut. 

When you put headers on and toss the heat riser valve away there is less exhaust manifold heat, and little to no pressure differential, so you don't notice anything happening because nothing is happening.

In some gasket sets there are intake manifold restriction inserts to promote a pressure differential. They are a band Aid to help emissions by bleeding some heat into the manifold all the time. You don't notice anything happening because the OEM carburetor is calibrated to match that reduced air density. We read the manual and gasket set instructions to figure that part out.

If the heat riser valve sticks shut then heat is applied all the time to the intake manifold, the engine runs hot, and you can crack heads and valve seats. If you keep running the engine you can crack the intake manifold at the belly section into the plenum internally. This causes all sorts of odd running, oil consumption, and hair pulling. 

The benefit of plugging a cylinder heads exhaust crossover ports with aluminum is those exhaust port bowls can then be ported identically to the others without that passageway equalizing exhaust flow. And you never worry about which side the gasket restrictors go on ever again. 

Good night. Ladd


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## Lemans guy (Oct 14, 2014)

Thanks Ladd, great insight......


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## armyadarkness (Dec 7, 2020)

Machinest-guy said:


> If you keep running the engine you can crack the intake manifold at the belly section into the plenum internally. This causes all sorts of odd running, oil consumption, and hair pulling.


This is and has been one of my concerns, from the beginning of my poor running problems (since they also seem to occur with heat). I've seen more than one cracked Pontiac intake, in my time. Weather is still holding me back, but I finally have all of my dizzy parts, so I can try the new vac can in a few days. Hopefully that does it.


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## Machinest-guy (Jul 19, 2019)

Best of luck to you. Why not test your manifold if you have any suspicion of it being cracked ? I make a pair of block off plates for the manifold sides. 5/8 plastic works fine or wood for that matter. Gasket with rubber mat from the hardware store. Hold them on the manifold flange with C-clamps. Put a hole in the plate where heat for crossover enters / exits. Make a plate for the carb mounting area the same way. Mount it with carb mounting hardware and add an air hose fitting so you can pressurize the manifold in a tub of water or use an A/C fitting if you have access to a vacuum pump. Fast - easy - cheap. The manifold should hold 30 lbs pressure more or less over night, or retain vacuum for at least several hours.


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## armyadarkness (Dec 7, 2020)

Machinest-guy said:


> Best of luck to you. Why not test your manifold if you have any suspicion of it being cracked ? I make a pair of block off plates for the manifold sides. 5/8 plastic works fine or wood for that matter. Gasket with rubber mat from the hardware store. Hold them on the manifold flange with C-clamps. Put a hole in the plate where heat for crossover enters / exits. Make a plate for the carb mounting area the same way. Mount it with carb mounting hardware and add an air hose fitting so you can pressurize the manifold in a tub of water or use an A/C fitting if you have access to a vacuum pump. Fast - easy - cheap. The manifold should hold 30 lbs pressure more or less over night, or retain vacuum for at least several hours.


I still have a pressure test jig from the two that I welded two in the past. I'm just waiting until after I get my vac advance verified. Hopefully, that cures the issue. If not, then many have suggested that the torque converter could also be too tight and causing my issue... fianllye, as I mentioned when I started the thread, the intake is also a suspect!


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Thanks Ladd, great insight......


I finally got a break in the weather and so I put on the new vacuum can. There was an extremely minute improvement. So, now it just barely stalls when I stop, were as before, it was dead before I even finished rolling. Again, the power of the engine is unbelievable, but it still wants to die when coming to a stop. It idles fine, idles fine in gear, and it wont die if I put it in neutral before stopping, but otherwise, same.


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## Lemans guy (Oct 14, 2014)

If you are close you might still be able to tune it out..the stall...again we are all remembering the converter...

so is it possible to enriched the mixture now that the timing seems to help a bit....via the mixture screws....


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## Lemans guy (Oct 14, 2014)

Remind me of base setting again and Centrifigal...was it 12 and 22....on the last test


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## Lemans guy (Oct 14, 2014)

To me it is acting just like an automatic trans that stalls at hard braking....the fix was an Anti-stall dashpot......you can look those up, lot’s of automatics had those in the 60’s... basically it is a plunger that prevents the throttle plate from slamming shut when you brake hard or pull your foot off the gas real fast.

many cars with automatic trans would stall at that point...

so one thing to try is to drive it and coming to a stop very slowly let up on the throttle pedal, very gradually and see if it still stalls...if it does not it may be that as the throttle is slamming shut real fast and causing a lean spike, a lean stall.....

opening the throttle screw a bit could help, enrichening the mixture could help if that is it

your timing was likely way out front too far advanced before......and when you came off the pedal it slammed the vac advance back on but way too much......

just possibilities


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## armyadarkness (Dec 7, 2020)

Yes the stall converter is definitely up on deck, just holding off until the timing is 100% squared away. 

I am tuning the mixtures for max vacuum, and then richening a bit more. However, repeated testing has shown no difference in where the mixtures are. 

I'm also considering high floats as a possibility, since the stumble and stall ONLY occurs at hard stops, however, it doesn't do it in neutral, so...

Base timing is 12 or better and with the vac can that you recommended I'm getting 22 at idle. Centrifugal is 22 and I appear to be getting mid 30's when pegged.

So, does it make sense to knock the mechanical advance down so that I can raise the base timing, or should I do the stall first and then resume?


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> To me it is acting just like an automatic trans that stalls at hard braking....the fix was an Anti-stall dashpot......you can look those up, lot’s of automatics had those in the 60’s... basically it is a plunger that prevents the throttle plate from slamming shut when you brake hard or pull your foot off the gas real fast.
> 
> many cars with automatic trans would stall at that point...
> 
> ...


You might be on to something;

I can DEFINITELY keep it from stalling when I brake. Moderate stops don't cause the issue and when fully stopped, Brake + Gas peps it right up... Neutral as well. 

As I mentioned, even though it runs rough as Hell and dies (or nearly dies) at that point, instant use of full throttle, roasts both tires... even at 10-12 MPH. So, it's not like it's loading up or bogging.


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## armyadarkness (Dec 7, 2020)

The dashpot Google definitely describes my issue, however it seems to only be discussed by the Mustang crowd. Holley makes one, but says that it's for a manual trans?


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## Lemans guy (Oct 14, 2014)

So agree on the too high floats....it could be ......and you could readjust and test....

the timing..12 + 22.....+10 on the vac is great....unless really weak springs in the dist are giving a fit, but I think you said all in by 3000 which should be good as well.

so you can try a few of those, just not all at once...

lower the floats and test..
Drop the base timing 4 degrees and retest
Open the throttle screw a tad and retest...

you got too high floats or to fast slamming shut of the throttle...that is why Insay maybe open a bit...sounds like you are close


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## Lemans guy (Oct 14, 2014)

Pontiac had them..just add Pontiac to your search


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Pontiac had them..just add Pontiac to your search


I tried. Found nothing, but I'll continue... My Dizzy springs are Moroso/ Silver Medium. I'll check the floats this weekend

Seems like Holley switched over to electric.









Holley 46-74 Holley Universal Throttle Solenoids | Summit Racing


Free Shipping - Holley Universal Throttle Solenoids with qualifying orders of $99. Shop Carburetor Solenoids and Brackets at Summit Racing.




www.summitracing.com


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## Lemans guy (Oct 14, 2014)

Try...1960 - 67 Pontiac carbuerator dashpot......may not be your carb...but they all act similar


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## armyadarkness (Dec 7, 2020)

Heres one that says it's an oem GTO part. Not much info on it. Does it just hook up with vacuum?






Dashpot,60-67 AFB Carburetor, 4bbl @ OPGI.com


Use with 4-BBL Carter AFB.




www.opgi.com


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> Try...1960 - 67 Pontiac carbuerator dashpot......may not be your carb...but they all act similar


It actually appears that all Carter equipped GTO's had one, which mine is.


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## deanhickey (Apr 6, 2015)

here is a NOS dashpot 1960-67 Pontiac carburetor dashpot, NOS! 7019951 carb GTO Bonneville Catalina | eBay


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## Lemans guy (Oct 14, 2014)

Thanks Dean...will that fit your carb Army....if so it may be worth a try


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## Lemans guy (Oct 14, 2014)

Yes vacumn diaphragm....just prevents the throttle from slamming shut gives it a soft landing to prevent stall..”Anti-Stall”....


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## 67ventwindow (Mar 3, 2020)

Lemans guy said:


> Thanks Dean...will that fit your carb Army....if so it may be worth a try


Is that instead of heal on brake pinkie toe on the gas.


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## Lemans guy (Oct 14, 2014)

Ha...Yes!....most hot Rodgers toss those things and try to dial in the timing and carb without it.....but some combinations of cam and TC etc may be easier with it.......

cheaper and easier to install than a new TC if it works...


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## 67ventwindow (Mar 3, 2020)

My Grandprix had this issue when in cold environments. Snow helped with weak rear brakes and one legged tire spun. I moved to fla seemed like the TC lossened up


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## Lemans guy (Oct 14, 2014)

I thought I had heard every reason to move to Florida before....

but a bad torque converter is as good as any!


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## armyadarkness (Dec 7, 2020)

So, are they adjustable? Still not getting many specifics from the manufacturers


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## armyadarkness (Dec 7, 2020)

And... since poor vacuum is an issue, should I consider one of the electric versions?


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## Lemans guy (Oct 14, 2014)

It does not use up much vacumn.....should be very small on that fixed diaphragm..

I saw that electric one as long as the function is the same, but I think there are different ones that are for AC cars that up the idle speed when the compressor engages....so when the AC switch goes on the electric solenoid goes on....that is not the same thing

although there could be some crossover function ..........the dashpot just gives a soft landing to the returning throttle....and then goes back to normal idle


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## Lemans guy (Oct 14, 2014)

Adjustable ..yes that stop is a screww on threads and you just screw it in or out for the qdjustment...the vac is just manifold vac


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## Lemans guy (Oct 14, 2014)

Some may just have a spring to slow the throttle....


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## Lemans guy (Oct 14, 2014)

Holley 2140 & 4000 Dashpot - Mikes Carburetor Parts


Holley 2140 & 4000 4 barrel carburetor dashpot. Used on vehicles with an automatic transmission. What is it for?



www.carburetor-blog.com





Here is some talk about a Holley one


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## Lemans guy (Oct 14, 2014)

PONTIAC V8 4-BARREL DASH POT ROCHESTER CARB 1963 1964 1965 1966 1967 | eBay


Find many great new & used options and get the best deals for PONTIAC V8 4-BARREL DASH POT ROCHESTER CARB 1963 1964 1965 1966 1967 at the best online prices at eBay! Free shipping for many products!



www.ebay.com


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## Lemans guy (Oct 14, 2014)

There is one... looks like it could work


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> I saw that electric one as long as the function is the same, but I think there are different ones that are for AC cars that up the idle speed when the compressor engages....so when the AC switch goes on the electric solenoid goes on....that is not the same thing
> 
> although there could be some crossover function ..........the dashpot just gives a soft landing to the returning throttle....and then goes back to normal idle


Ah... That was the problem that I was finding in my reading yesterday... Many folks claiming that it pulled double duty, others demanding that it served one or the other. Either way, it "seems" like it's for engine load.


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> There is one... looks like it could work


Very interesting. Since I have the Edelbrock carb, I'm searching for a Carter mount. With luck it would just bolt on. If not, I'll adapt one the Qjet or Holley ones.


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## armyadarkness (Dec 7, 2020)

This one says that it's for 67 Pontiac Rochester and Carter, so I ordered it. I'm sure I'll have to fab a bracket.








NORS Carb Dashpot; 1957 thru 67 Pontiac w/ Carter & Rochester 4bbl - GM 7026093 | eBay


Find many great new & used options and get the best deals for NORS Carb Dashpot; 1957 thru 67 Pontiac w/ Carter & Rochester 4bbl - GM 7026093 at the best online prices at eBay! Free shipping for many products!



www.ebay.com


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## armyadarkness (Dec 7, 2020)




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## Jd70 (Jul 4, 2019)

Well I’m getting a little weary holding on to the edge of my seat !! What happened next ?? Is the issue resolved ? Inquiring minds want to know.
Thanks
JD


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## armyadarkness (Dec 7, 2020)

Funny that you should mention it... Because last night I began the final stages of resolving this all. 

To recap:

Pontiac 400 with a fresh rebuild
670 heads
HEI dizzy
Edelbrock 800 avs carb
Vacuum seemed to be the culprit. My vacuum was very low, which I thought was because of the cam, but it was not. The vacuum was so low because I adjusted the rockers with the engine warm, but off. It has been suggested in many places that it's an acceptable method, and I've always used it in the past... It is not an acceptable method!

The lifters were bleeding down when I was adjusting the rockers, so the valves were too tight and hanging open. I never equated that with vacuum, but sure enough, after re-adjusting the valves with the engine running, my vacuum went from 10-12 up to 18-20. That problem of stalling after a hard stop has been solved. FYI, many users in this thread suggested early on that I adjust the valves while running, but since I never had any issues, I did not listen to them.

So now the stall is cured, but the power is way down! So I'm wondering if the valves hanging open was working like a cam?

I bought a billet dizzy with fully adjustable total timing, vac, and curve, so I'm tweaking the timing now, and when that's done, I'll tweak the jetting on the carb.

When it was stalling, if I nailed it off the line, it went insane. And then from a roll on, any full throttle below 20-30 MPH, broke the tires loose and chirped 3rd. Now with the valves set right, off the line performance is sluggish and roll on is a little underwhelming. 

During my timing checks last night, I set the base to 18 and was reading a total at about 300 rpms of 36. Since the dizzy has a 21 bushing in it, total SHOULD have been 39. The vac can was giving me another 12, for 30 at idle. But there was no pinging... and that with fresh 670 heads and 93 octane.

So, either my engine just loves timing, or the balancer has slipped zero... or the dial back timing light is poo... or the dizzy is not putting out up to spec.


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## Jd70 (Jul 4, 2019)

I take it your rockers are not stock Pontiacs set by torque.

JD


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## armyadarkness (Dec 7, 2020)

Jd70 said:


> I take it your rockers are not stock Pontiacs set by torque.
> 
> JD


The general consensus was that poly-lock nuts should always be added, and then after that, you really need to set them manually, to zero lash. I'm sure that most would argue that even the torque to spec rockers, was not a great idea.

My engine has a roller cam and lifters, so I also added the roller rockers. It's such a cheap and easy way to add life, horsepower, and cooling.


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## Old Man Taylor (May 9, 2011)

Not zero lash. Most lifter manufacturer's recommended adding 3/4 turn from zero. I typically go 1/4 turn past zero.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> Not zero lash. Most lifter manufacturer's recommended adding 3/4 turn from zero. I typically go 1/4 turn past zero.


Same... I go 1/4, but in my case that was on a bleeding down lifter, so it was too much.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> Not zero lash. Most lifter manufacturer's recommended adding 3/4 turn from zero. I typically go 1/4 turn past zero.


Jim,

Is there any point in having a vacuum gauge connected while setting valves? I suppose not, but I did have one connected and I was able to see the difference in vacuum as I adjusted.


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## Jd70 (Jul 4, 2019)

Hmmm. I’m glad to hear its running better.
Zero lash in hydraulic lifters is when it goes quiet while running. 
Adjustment . As you go past quiet to 1/4 or 3/4 turn the lifter internal plunger is “bleeding or leaking down” excess oil beneath the plunger, it has to. You are centering the plunger in its travel range within the lifter body, preloading it per se. Torqed adjustment has taken into account for length and geometry and has predetermined the pushrod length to accomplish the centering of the plunger. Now if your lifter didn’t leak or bleed off excess oil during adjustment, this would cause valves to not seat and in extreme cause damage. If your lifter plunger is defective and continuously leaking down it’ll never go quiet, or make a lot of noise until or if it ever “pumps up“, to zero lash. I’m not getting the correlation to a decrease in power or increase in vacuum because the lifter adjustment is not changing the cam lobe, nor cam timing. Unless the lifters were so preloaded as to have lost all oil under the plunger and in essence creating a mechanically solid lifter, but your pushrod geometry would be way out, and the valves wouldn't seat and poor running backfire would result. And that is an iffy scenario happening at best.
Still inquiring
JD


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## armyadarkness (Dec 7, 2020)

Jd70 said:


> Hmmm. I’m glad to hear its running better.
> Zero lash in hydraulic lifters is when it goes quiet while running.
> Adjustment . As you go past quiet to 1/4 or 3/4 turn the lifter internal plunger is “bleeding or leaking down” excess oil beneath the plunger, it has to. You are centering the plunger in its travel range within the lifter body, preloading it per se. Torqed adjustment has taken into account for length and geometry and has predetermined the pushrod length to accomplish the centering of the plunger. Now if your lifter didn’t leak or bleed off excess oil during adjustment, this would cause valves to not seat and in extreme cause damage. If your lifter plunger is defective and continuously leaking down it’ll never go quiet, or make a lot of noise until or if it ever “pumps up“, to zero lash. I’m not getting the correlation to a decrease in power or increase in vacuum because the lifter adjustment is not changing the cam lobe, nor cam timing. Unless the lifters were so preloaded as to have lost all oil under the plunger and in essence creating a mechanically solid lifter, but your pushrod geometry would be way out, and the valves wouldn't seat and poor running backfire would result. And that is an iffy scenario happening at best.
> Still inquiring
> JD


Valve adjustment is one of those things... like asking which carb is best... Everyone has an opinion on it, and some even swear to it, yet even the experts vary widely in their instructions on "the best way". 

Far be it from me to ever know what the Hell I'm talking about, but the way that I did the valves, cold, was how I have done them for 35 years and I never had issues before. There are also many articles on the web, advocating that method... but I won't be using it in the future.

In my case, the car wouldnt idle (I assume) because it didn't have enough vacuum to pull fuel into the cylinders. So if the exhaust valve was hanging open, while the intake valve was attempting to import fuel, then I could see that being a big issue.

And of course, if the intake valve was hanging open, it would allow more fuel into the cylinder, much like a cam.

However, this is all just my theory on why it happened and acted as it did.

At the end of the day:

The car stalled under hard braking and it wouldn't idle, but it ran like a top fuel dragster, outside of those conditions. 
It was down almost 10hg of vacuum. 
Adjusting the valves raised the vacuum and cured it.
Now I seem to have lost some of that improved performance on the mid and top.


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## Old Man Taylor (May 9, 2011)

armyadarkness said:


> Jim,
> 
> Is there any point in having a vacuum gauge connected while setting valves? I suppose not, but I did have one connected and I was able to see the difference in vacuum as I adjusted.


No. Do it running and go 1/4-3/4 turns passed the point where the noise is minimized. The challenge running is keeping the oil in the head. I use a cut off valve cover. If you just make holes in the valve cover that is good enough. If you cut one in half then you will need the rocker clips to keep the rockers from squirting oil out where you don't want it.


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## armyadarkness (Dec 7, 2020)

The vaales are already done now, and fortuantely, my engine builder was a long time Pontiac guy, so he put oil restricting push rods in. You can run it without getting oil anywhere.


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## JesseLyon (Sep 13, 2020)

Since swapping out my Edelbrock 4bbl to a stock ‘66 tri-power (on my ‘65 GTO, 4spd, power brakes) I’m having the same stalling problems on hard braking. Runs great and idles fine in neutral, hot and cold, but when I hard brake car while driving, car will stall out right away. It’s driving me crazy! Going to try new fuel filter, PCV valve and grommets tomorrow (intake and brake booster), but trying to follow the thread to see if anything else might help. Valve adjustment maybe too?


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## armyadarkness (Dec 7, 2020)

Well in my case, it was the valves, but all of the things that I repaired a long the way, yielded a much nicer running car


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## JesseLyon (Sep 13, 2020)

armyadarkness said:


> Well in my case, it was the valves, but all of the things that I repaired a long the way, yielded a much nicer running car


Looks like I need to grab a coffee and dig into this epic long thread!


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## armyadarkness (Dec 7, 2020)

JesseLyon said:


> Looks like I need to grab a coffee and dig into this epic long thread!


114 proof bourbon would be better. What is your vacuum? That's the tell tale.


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## JesseLyon (Sep 13, 2020)

armyadarkness said:


> 114 proof bourbon would be better. What is your vacuum? That's the tell tale.


Going to pick up a vacuum gauge today to find out. Was fine with the 4bbl/aluminum intake setup, but obviously somethings changed with the tri-power/cast iron intake setup. Problem is, I cant drive the car with the vaccum gauge hooked up...so not sure how to go about that. Problem only seems to occur while Im driving and braking during a hard stop. Cant recreate the issue while stopped and pressing the brake hard


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## armyadarkness (Dec 7, 2020)

JesseLyon said:


> Going to pick up a vacuum gauge today to find out. Was fine with the 4bbl/aluminum intake setup, but obviously somethings changed with the tri-power/cast iron intake setup. Problem is, I cant drive the car with the vaccum gauge hooked up...so not sure how to go about that. Problem only seems to occur while Im driving and braking during a hard stop. Cant recreate the issue while stopped and pressing the brake hard


You don't need to drive the car with the vac gauge connected. Just hook the gauge up to the carb and see what your idle vacuum is. If your car ran fine before, and you didn't mess with the dizzy or valves, then it's probably either a vacuum leak or float level. It's easier to check vacuum than its float level, so...


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## JesseLyon (Sep 13, 2020)

armyadarkness said:


> "Well, I don't want to hijack this thread, but if I understand you correct, you're just running the center carb on a six pack? Hit me up in the stalling thrread "


Re comments on other thread....I just meant when Im off throttle/idling its only running on center carb (outer carbs dont kick on until you are fullly on throttle), which is maybe creating less overall vaccum then when I was running the Edlebrock 4 barrel carb/intake, which I had no vacuum issues with. I realize a vacuum leak could be coming from any one of the three carbs, PCV, brake booster....just need to narrow down exactly where. My thought was also that crossover exhaust pipe might help to create more scavenging/backpressure/vacuum....but its all a shot in the dark until I get the vacuum gauge.


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## armyadarkness (Dec 7, 2020)

JesseLyon said:


> Re comments on other thread....I just meant when Im off throttle/idling its only running on center carb (outer carbs dont kick on until you are fullly on throttle), which is maybe creating less overall vaccum then when I was running the Edlebrock 4 barrel carb/intake, which I had no vacuum issues with. I realize a vacuum leak could be coming from any one of the three carbs, PCV, brake booster....just need to narrow down exactly where. My thought was also that crossover exhaust pipe might help to create more scavenging/backpressure/vacuum....but its all a shot in the dark until I get the vacuum gauge.


Got it. Once you read your vacuum, you'll know instantly if that's the issue. Yes, x pipes help and work, which is why theyre such a popular upgrade. I don't see them helping vacuum though. Between 3 carbs and an intake swap, I'm leaning toward vacuum leak.


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## JesseLyon (Sep 13, 2020)

armyadarkness said:


> Got it. Once you read your vacuum, you'll know instantly if that's the issue. Yes, x pipes help and work, which is why theyre such a popular upgrade. I don't see them helping vacuum though. Between 3 carbs and an intake swap, I'm leaning toward vacuum leak.


OK, so heres what Im seeing with some video reference...

Vacuum at idle with brake booster disconnected is around15/16...





Vacuum at idle with booster connected drops down to 10-12....(apologies for the tilted video)






Vacuum while driving seems ok, but you can see when I hit the brakes hard, vacuum drops to almost 0 and nearly stalls out....(phone fell off dash a few times, time to get a mount )






So all told, I guess this points to a leak at the brake booster. I am also seeing a bit of brake fluid dripping down the front of the booster too, so I guess its time to spend some money. Is there a kit available just for the seals on these, or would people here recommend swapping out the enitre booster and/or master cylinder?


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## 67ventwindow (Mar 3, 2020)

This place has booster rebuild kits seem to be twice the price or a rebuilt one. Power Brake Booster Repair Kits-Fusick Automotive Products, Inc.
RockAuto and other have the master cylinder seals.


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## JesseLyon (Sep 13, 2020)

67ventwindow said:


> This place has booster rebuild kits seem to be twice the price or a rebuilt one. Power Brake Booster Repair Kits-Fusick Automotive Products, Inc.
> RockAuto and other have the master cylinder seals.


Wow, ya, seems like I could replace the whole thing for the same price.


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## Lemans guy (Oct 14, 2014)

Either way you have to remove it, just swap for a new or rebuilt unit and you you should be good.


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## armyadarkness (Dec 7, 2020)

JesseLyon said:


> OK, so heres what Im seeing with some video reference...
> 
> Vacuum at idle with brake booster disconnected is around15/16...
> 
> ...


I can't see the videos, but it seems like you solved it!


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## JesseLyon (Sep 13, 2020)

armyadarkness said:


> I can't see the videos, but it seems like you solved it!


For some reason the videos still werent set to Public. I think Ive fixed it properly now if you were interested in seeing them. Maybe you can see something else that I missed. Vacuum seems to be a bit lower then it should at idle, and drops a lot when braking hard.


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