# 1970 GTO #13 Heads YS Block 461 Stroker Kit Comp HYD Cam BP8021SP



## GIgtoGuy (Jun 24, 2021)

Started this new thread to try to get some assistance timing and carburetor tuning etc. Engine has 300 miles and Oil and filter installed…but extremely sluggish nothing near what I expected. It’s the original 1970 YS block with the original distributor and external coil, points have been removed and a pertronix ignition installed. Vacuum advance was unplugged by the engine builder to better control the timing he said. The carburetor is the original Quadra jet and he said he changed the jets but I have no idea what to. I’m running NGK racing plugs heat range 7. Engine vacuum is at 15 in park idling and 12-14 when I drop it in gear and goes up to about 20 at 2500 RPMs.


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## GIgtoGuy (Jun 24, 2021)

OK got the spark curve to come in around 3000 RPMs and total timing is now 36. So timing at idle at 22° at 830 RPMs. Plugged the vacuum advance back in and took it for a drive and it runs much better pinging has stopped. Power is up. What about carburetor adjustments? Any and all advice would be appreciated.


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## BearGFR (Aug 25, 2008)

When you say "total" is 36 @ 3000. Is that with or without the vacuum connected? 
(Should be without - in fact everything you do with a timing light should be with the canister disconnected and the line plugged. The one exception to that being MEASURING how much advance the can adds) 

Bear


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## GIgtoGuy (Jun 24, 2021)

All the measurements I did was with the vacuum advance unplugged. I never measured any timing after plugging it back in.


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## BearGFR (Aug 25, 2008)

Awesome - just double checking. 22 initial sounds like "a lot" but if it's running good and not hard to start, I reckon it's ok. 

Bear


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## GIgtoGuy (Jun 24, 2021)

OK double checked my numbers. Base timing is 20° at 800 RPMs. Total timing at 36°. Total timing is all in around 3000 RPM. All numbers were done with vacuum advance unplugged. So centrifugal would be 16° 15 Hg of vacuum at idle. 12-14 Hg with the brake on in gear.

So wondering if this means anything when I plug the vacuum advance in the idle jumps to about 950 RPMs and then the base timing jumps to about 40°. And with the vac can plugged in and I when I rev past the 3000 RPM mark my timing light is showing about 60° of total timing. What the hell is going on here ?? I thought the vacuum advance didn’t add timing when total mechanical in the distributor took over? Is my vacuum adv can bad? Also the timing mark jumps around a bit is this a sign of distributor malfunction or normal?


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## BearGFR (Aug 25, 2008)

No, your can isn't bad and nothing is wrong. The vacuum canister adds advance any time there is manifold vacuum present. That's what it's supposed to do. The only times there is (close to) zero manifold vacuum is when the engine is off (lol) and when it's at wide open throttle under full load. You will not be able to duplicate that condition with the car sitting in your driveway so even if you blip the throttle wide open briefly you won't be able to create a 'zero vacuum' condition, so you'll always see the can adding some advance. This is why you always disconnect it when setting timing - that's the only way to completely take it out of the picture with the engine running in neutral. 

Mechanical advance never "takes over". It's always there and is a function of engine RPM. The vacuum canister adds MORE advance on top of what the mechanical system puts in, any time there is manifold vacuum present. Manifold vacuum varies with engine load: the less the engine is loaded, the more vacuum there will be.

Since you said that connecting it at idle is adding advance and causing your RPM to go up (which is also normal), that tells me that you're connecting the vacuum advance to a 'non-ported' vacuum source. I.E. one that always "sees" vacuum. The other option is to use a ported source. A ported source is one that is taken from above the throttle plates in the carb, so that it doesn't start to "see" significant vacuum until the throttle plates are opened. Not every carb has both. For instance the AED carb I have on my car does not have a ported source.

Whether you use a ported or a non-ported vacuum source for the advance can is one of those topics that tends to devolve into a "Hatfields vs McCoys" arguments with people adamantly advocating one side or the other. My opinion is that you should try both if you can, then stick with whichever one your particular engine seems to like the best.

But, no --- everything you described sounds perfectly normal to me.

Bear

p.s. About your jumping timing marks. That CAN be an indication of a distributor problem, for instance if the end play on the distributor shaft is too loose and needs to be shimmed, or if there's something loose/worn inside the distributor itself, or if the triggering mechanism (points, etc.) has gone wonky. It can also happen if the inductive trigger on the plug wire isn't always picking up the spark. It's sort of a question of "how bad" it is and how much it's moving around.
There's a spec for shaft end play but I forget what the specific measurement is. I know it's "out there" on the Interwebs "somewhere". Remove the cap and see if you can pull/push the rotor "up and down" and by how much. There has to be SOME slack in there to allow for heat expansion.


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## GIgtoGuy (Jun 24, 2021)

OK here’s where I get confused. The vacuum lines are all hooked up according to the original diagram. There’s a three tee split on the rear of the carburetor and the bottom. One line goes inside the car the second to the brake booster the third to the vacuum advance. I’m not sure I have a ported source but if I did wouldn’t that also create too much advance under wide-open throttle? I just disconnected the vacuum advance and plugged it and went out and took it for a drive and my god!! it runs like a new car! This tells me the vacuum is not completely going away under wide-open throttle and is adding too much timing. So what now? I feel like I should be running the vacuum advance instead of unplugged.
Thanks again for all your help!


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## BearGFR (Aug 25, 2008)

If the can is tee'd into that fat hose that goes to the brake booster, that's definitely an un-ported source. There's no difference in "how much" manifold vacuum is present between a ported or a non-ported source. The only difference between them is when they "turn on". A non-ported source is always live, but a ported source doesn't 'activate' until the throttle blades open. Both will drop to near zero under WOT and will be exactly the same. Vacuum is never ACTUALLY zero because if it was, no air would be flowing into the engine. It just gets very very low - well below the amount needed to activate the vacuum can.

I don't remember - which carb are you running?

P.S. - I just closed the other thread you've been posting on. Please continue on this one only. It was getting too confusing.


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## GIgtoGuy (Jun 24, 2021)

ok yes I was getting confused as well…sorry… I have the original quadrajet carb. If vacuum is near zero at WOT why would the car run so much better when the cans unplugged


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## Lemans guy (Oct 14, 2014)

Bear is giving you all good advice here. Let me add a few things. Yes your vacumn can is wrong,…it is probably pulling 20 to 25 degrees of advance over your 36. This is vary common and what we all take out to curve a distributor correctly.

You want a can that will pull 8 to 12 degrees at the crank. 10 is the middle. That is all the vac advance you want, you have much more. Not unusual, I see this on most distributors that I curve. So you need to get it to 10; degrees.

Not only does it pull too much timing, but it also does not operate under your vacumn reading of 12 in drive at idle. The can you have likely is “dithering” in and out because it is set up to be fully deployed at a higher vac level…too much movement. You want a can that stays locked in and gives you the magic ten degrees at idle and during light throttle cruise. It then will drop out when the vac goes below 5HG ……and you are back to 36….

When set right you will have a max of 46 not 60 for light throttle cruise.
The weights as Bear said are RPM dependent only, the vac can is not connected to them..

as RPM’s rise the Centrifigal weights go out and give you that 16 more degrees…..

also as RPM’s rise vacumn is dropping, and once it gets low enough it adds no more timing. They cross in effect…one is going up the other down,but both can be fully deployed if RPM’s are up,…in your case 3000 and vac is above the rated limit of the can, say 11HG.

That is where you can see the 46…..of course carb, AFR, jets all effect this as well.

so remind me do your have a coil in cap HEI wide body distributor, or a narrow body distributor with external coil, like the old points style? Let me know and I will tell you how to fix your vac can


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## Lemans guy (Oct 14, 2014)

The dithering vac can may be the cause of your timing mark jumping around, as it “dithers” it is constantly changing timing.

As Bear said it could be other things like shims on the distributor gear.

on an aluminum distributor.005 to .007 is the proper shaft end play

On a cast iron distributor .010 to .015 is the shift end play……if way off of those you can get moving timing marks and hunting idle as the shift moves up and down.


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## GIgtoGuy (Jun 24, 2021)

now it’s starting to make more sense. I have a narrow body distributor with external coil. The point style with pertonix ignitior. It does have some play in the distributor but doesn’t seem like much. I don’t have a magnetic base with dial indicator to measure how much it’s moving. I have considered a new distributor with an adjustable vac can to limit it and maybe that’s the way to go to resolve any distributor issues I’m having.


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## Lemans guy (Oct 14, 2014)

Don’t get an adjustable cam, they only change the rate of vacumn and not the amount of timing. First thing I do is take those off any distributor I curve. I have a box of them.

with your setup this can will work great. It is one of my favorite and will go with your low vacumn.

all the cans are made by standard motor parts (SMP) but different vendors have different part numbers

Rock auto calls it a Standard Motor Parts VC-181
Oreilly part # is BWD V375
NAPA part # is VC 1808

specs are 5 to 7 HG. 8*@ 11 - 13

This Mayans that the vac can starts pulling vacumn timing at 5 to 7 HG and pulls all of its timing which is 8 degrees distributor ( which equals 16* @ the crank) and pulls it all in by 11-13 Hg.

Now 16 degrees at the crank is too much, but there is no vac can sold that pulls less than this. So you will need to email Lars at ……[email protected]……..and ask to buy one of his vacumn correctors. It costs about $14.

This corrector will both knock the vacumn timing back to 8 to 10 degrees and lower by a small amount that high vacumn number. Because it limits the travel of the vac can rod all of the 10 degrees will pull in by about 9 or 10 Hg, which is lower than your idle vac….you said it was 11 or 12 as I recall.

Now I would recommend that you take a small pliers and just stand it straight up in the vertical part of the stem and just put a slight pressure on the stem toward the can. You can’t even feel it move, but it should give you enough to make the can pull 8 degrees with Lars corrector.

Then plug tha vac can to full manifold vac. I set them all that way. That should give you 28 degrees of idle timing, yes it can idle there ok. The hotter the cam the more idle timing it can take, you should be ok. The Petronix on most models, check yours, call their tech line, will reduce cranking timing by 4 degrees to prevent kickback. So it will crank at 24 degrees.

You can try it here and see how you do. It should idle smooth and have good light pedal response as well. You could use ported vac, some guys do but it will be the same on acceleration and same drop out at wide open throttle. If your cam is hot, do it on full manifold vac.

Always check for pinging by listening and checking the plugs for tell tale signs of aluminum flecks. Stay with it you are getting close!


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## GIgtoGuy (Jun 24, 2021)

Awesome! I’m on it! I will follow up when complete! Thanks for your help! I really appreciate it!!!


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## Lemans guy (Oct 14, 2014)

Shaft end play is easily fixed, yours may be okBut if you need to Moroso sells a hardened shim pack # 26140 ( summit/JEGS) about ten bucks, just use a feeler gauge and get it close, this is not engine bearings.

many distributors could use these shims, but generally the large bronze shaft bearings do not need to be replaced, and if they do, it would be easier to just replace the distributor, unless it is desired as an original part. I would just check the end play and use the shims if needed.

You just knock out the roll pin on the distributor gear, and replace the shims. Put the thin ones in the middle. Before you remove the distributor gear locate the dimple on the gear. That dimple is placed on the same side of the rotor tip. It is a balance to the tip, small amount of metal was removed to counter balance the rotor tip.

early distributors this also helped orientate the dist so the vac can would not hit the intake when setting base timing. Just note the dimple and set it back right.

good luck let us know how you do!


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## GIgtoGuy (Jun 24, 2021)

The car is running awesome! Thank you for all your help. I have made an appointment in two weeks with a chassis Dynk to fine tune and optimize performance. Again I appreciate all your help. 🙂😜😎


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## GIgtoGuy (Jun 24, 2021)

Next issue is idle when I turn on my air conditioning. Do any of you guys use high idle solenoids to increase the idle when you turn on your AC? I can’t compensate with the idle screw. I have to turn the idle up to about 1100 RPMs with AC off to make the car idle in gear when the AC is turned on. That’s way too high when I drop it in gear. Any suggestions


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## GIgtoGuy (Jun 24, 2021)

Another thought that just came to mind is if I switch my vacuum for the dizzy from ported vacuum to manifold vacuum would that possibly help keep my idol up during AC on situations? I did notice when I’m running manifold vacuum for the distributor that my idol is significantly higher and cannot be turned down with the idle screw below about 900 RPMs.


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## BearGFR (Aug 25, 2008)

A ported source will DELAY the can "coming on" until after the throttle begins to open, so if you're having an idle problem with the A/C on, switching to a ported source will only make that worse.

There's a sequence to getting things all dialed in, and the order matters.
First: Get your fuel delivery/fuel mixtures right during all modes of operation, in this order (best to use an accurate air/fuel meter):
1) WOT mixture (shoot for "about" 12.5:1)
2) Cruise mixture (upper 12's, low to mid 13's)
3) Accelerator pump (no bog when you hammer it from idle)
4) Idle mixture (high 13's, even low 14's -- or wherever manifold vacuum is at maximum)

THEN (and only then) move on to ignition.
Second: Get your mechanical advance curve right - this is what determines how it runs under full power / wide open throttle.
Third: Once that's done, fine tune your "light cruise" operation with the vacuum can. You want "enough" to help with engine cooling and fuel "economy" (yeah right, economy with these cars...)
Last: Deal with whatever issues remain at idle, if there are any. If everything else is correct and you still have a problem with it wanting to stall with the A/C or other heavy load (like big electric fans), consider adding an idle solenoid to add a little throttle whenever either of those is on.

Sometimes, especially with idle, you'll have to go back to a previous step to re-dial things in. For example, adding rpm will increase air flow which can cause it to pull more fuel through the idle mixture ports which will enrichen the mixture.

The keys to nearly all of this is to address one thing at a time, in the right order, and to make small incremental changes while paying attention to the results. Your engine will tell you what it wants and in which direction to 'turn the knobs', you just have to learn how to listen to what it's trying to tell you.

Bear


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## GIgtoGuy (Jun 24, 2021)

you have your own shop I’ll bring you the car and you show me this is exhausting 😩


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## GIgtoGuy (Jun 24, 2021)

is there such a thing as too much initial timing? I have the Edelbrock Proflow4 and I have it running good but I am unsure where exactly to set my initial timing as it seems to run the same at 12 than it does at 20? Any input would be great


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## PontiacJim (Dec 29, 2012)

GIgtoGuy said:


> is there such a thing as too much initial timing? I have the Edelbrock Proflow4 and I have it running good but I am unsure where exactly to set my initial timing as it seems to run the same at 12 than it does at 20? Any input would be great


Your Initial, wherever you move it, affects your Total. So if you have 20 degrees Initial and 36 Total then drop down to 12 degrees Initial (8 degree drop), your Total will also drop down 8 degrees to 28 Total. And same any time you make any adjustments up or down with the Initial - so then you have to change the timing curve accordingly. BUT, if you had 12 Initial and 36 Total, and bumped it up to 20, guess what, your Total is now 44 degrees and I would say it is a matter of time before your damage your engine due to detonation.

If the engine runs good at 12, then leave it. Some engines run best at 6, some at 9, yours at 12, some at 21. Just depends on the engine build.


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## GIgtoGuy (Jun 24, 2021)

Thanks! That all makes sense. However with this EFI kit I can set initial, advance and total all individually without affecting the others. I have the total set at 34 and the advance at 10. I have played with different settings for the initial but sense no difference in engine performance or idle between 12 or 20. That’s why I ask the benefit of either or…


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## PontiacJim (Dec 29, 2012)

GIgtoGuy said:


> Thanks! That all makes sense. However with this EFI kit I can set initial, advance and total all individually without affecting the others. I have the total set at 34 and the advance at 10. I have played with different settings for the initial but sense no difference in engine performance or idle between 12 or 20. That’s why I ask the benefit of either or…


OK, you settings look good.

The EFI manages the air/fuel better than a carb, so I think that is where the differences might be with regards to the Initial. The more Initial can make the engine more responsive when you crack the throttle open and additional gas is introduced via the accelerator pump/squirters on a carb equipped cars so you don't get a big bog when extra raw gas is introduced through the squirters and the car goes flat before picking back up.

And generally, as you increase the timing advance on the Initial on a carb car, it will cause the RPM's at idle to increase,so then your idle speed has to be adjusted taking into account the increase in advance. Idle speed can also be connected to cam selection with the larger cams having more overlap need more idle speed because engine vacuum is much lower and won't pull in a good charge of air/fuel unless idle speeds are raised higher to compensate and keep the air/fuel mixture velocity speeds up - engine will stall/choke out otherwise.


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## GIgtoGuy (Jun 24, 2021)

Ahh..ok that makes sense. Thank you 🙏


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