# Stumbles at WOT



## Cmeyer9424 (May 5, 2020)

Hey y’all so I’ve been trying to get this issue figured out since I bought the car a few months back. Either from a dead stop or cruising around if I put the pedal to the floor the car stumbles and sounds like it wants to die but doesn’t, even had a small back fire through the carb. If I ease into it
it’ll go but it feels like it’s not giving all it’s got.

It has a Holley 750 double pumper which I just replaced both accelerator pump diaphragms in. Before this, if I put it to the floor it would completely die. I have also put a vacuum gauge on it and adjusted all four idle mixture screws to achieve best vacuum which I believe was around 25 at the manifold. I also found that if I work the throttle linkage at the carb and snap it to wot it doesn’t seem to have any stumble or hesitation. 

The car came with the 400 with the Holley 750, Edelbrock aluminum heads, beefy looking rockers, a good sounding cam, and long tube headers. I’m not sure of any of the specs since I was unable to get the build sheet for the upgrades. I just feel like this setup really should have some get up and go but it can’t get out it’s own way!

I can also try and upload a video if that would help

Any input or advice would be great!! Thanks!


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## BearGFR (Aug 25, 2008)

"Working the throttle" at the carb won't tell you anything or mean anything because in that situation there's no load on the engine.

There are references all over the internet about how to set up Holley carburetors, and a handful of those even have useful information (lol) - so you might do some searches on your symptoms. Because changing out your pump diaphragms "changed something", that suggests that you're in the right ballpark. Make sure your pumps are adjusted properly (internet references), your power valve (valves, if it has two) don't have ruptured diaphragms, and also that your ignition timing is correct. Getting the correct timing is more than just setting it to the factory 6-degrees initial and forgetting about it. There are other posts on here detailing the process.

You may need different pump cams to either speed up or slow down the pump shot, larger (or smaller) pump nozzles. The trick is to make small changes, test, understand what effect the change had, and act accordingly.

Getting a Holley set up correctly isn't as simple as everyone makes it out to be, I know from direct personal experience. It really helps to understand all of the carb's internal systems and how they're supposed to work, how they can be expected to respond to changes, how to interpret what your engine is telling you, etc. There are books available that have that information.
A vacuum gauge like it sounds like you already have is invaluable. Also very helpful is a wide band air/fuel meter, either a hand-held one or a permanently installed one.

Go ahead and buy yourself a tall stack of bowl and metering plate gaskets and get familiar with removing, disassembling, reassembling, and reinstalling it because there's a good chance you'll be "into it" multiple times by the time you get it right.

Start by make a record of everything you can: primary and secondary jet sizes, pump cam, pump nozzle sizes, power valve specs (stamped on the valve), idle air bleed sizes (if removable), high speed air bleed sizes (if removable), idle feed restrictor sizes and location, how much of the transition slots are exposed when the throttles are "closed" (idle setting), power valve restrictor channel sizes (if tunable)... everything you can measure or examine.

Keep a record of every change you make and what happened. (I used a spreadsheet for all this)

Back to your original problem...

If we ASSUME that your ignition timing is correct (again, verify it first), and your power valve(s) aren't leaking, and everything else is in good order (no vacuum leaks, etc.) the behavior you're describing is probably because the accelerator pump shot isn't "right".

It can either be too rich / too much / too "quick" or too lean / not enough / too slow. Both conditions can cause what's happening. Watch your mirror or have a helper watch when you 'stomp' it from cruise. Does it 'go' for a fraction of a second and then fall on its face or does it stumble immediately? Is there a puff of black smoke out the exhaust? What happens if you roll into the throttle as opposed to hitting it all at once. Can you find a rate where it doesn't stumble as long as you don't hit it any 'quicker' than that? These answers all help you determine if your engine is wanting more or less pump shot. Different pump cams control the timing and volume of fuel (to a degree). Pump nuzzles control the duration of the shot. Larger nozzles put out more volume quicker, but the duration of the shot won't be as long. Smaller nozzles "slow down" the shot over a longer period of time. If you find out that your engine is wanting a LOT more fuel from the pump shot, you may have to move up to the larger 50cc pumps on the secondaries, primaries, or both. 

Every combination is different and what works for one Pontiac 400 may be horribly wrong for Pontiac 400. It's a process. That's why it's called "tuning".

There's a guy over on PY, Tom Vaught, who's an expert and has helped a lot of people. He helped me a lot when I was doing battle with mine.

Bear


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## Old Man Taylor (May 9, 2011)

My first suspicion would be the power valves. If it has a cam that lowers the idle vacuum, then you need lower numbered PV's.


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## GTO44 (Apr 11, 2016)

Old Man Taylor said:


> My first suspicion would be the power valves. If it has a cam that lowers the idle vacuum, then you need lower numbered PV's.


If it stumbling at w-o-t where theres no vacuum then the power valves are already open no matter what size they are.

I would do as Bear suggests and work on your accelerator pump sizes. Sounds like its not getting enough fuel and you have a lean backfire condition. If it was too rich you would have more of a bog than a stumble with backfire thru the carb. What size accelerator pump nozzles do you have in it currently? If you’re already at number 35’s then you need to up the pumps to the 50cc version Bear referred to in order to go to a bigger nozzle size.

Changing the accelerator cam size will help when you’re getting on it but not at full throttle or rolling into the throttle until w-o-t. When you stab the gas all way to floor instantly, it doesnt matter what cam type is in it the pump shot is at 100% immediately.

Assuming cruising conditions feel fine i would leave the primaries alone And possibly give it a little bit bigger jet size in the secondaries in addition to more pump shot.

Again as Bear stated you’ll have to play with it allto really dial it in. Make one change at a time until you get the results you’re looking for.

Also whats your timing curve look like?


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## Cmeyer9424 (May 5, 2020)

Thank y’all for all the info!! It’s definitely a lot to consider, it’s been a long time since I’ve done anything with a carb. I believe that the pump nozzles are 31 but I will check this afternoon. When I put my timing light on it at idle it is past the factory marks on the balancer by a little maybe 15 or so since the last mark is 12. When I get the rpm up high enough to where it stops advancing, with the vacuum advance off the distributor and plugged, the timing light dial is set to about 32 when it goes back to 0 on the balancer.

Also, when I roll off idle just a bit and give it gas it seems to kind of sputter but not bad. As for putting it to the floor it instantly stumbles no delay.
I had my wife work the throttle last night while I looked at the linked and when she held it to the floor I noticed I had about an 1/8” more throttle available that the pedal wasn’t using.

When I get it out next I’ll take a video of it at wot

Hope I am explaining this all right haha!
Thanks again for all the info


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## Mine'sa66 (Oct 30, 2019)

About a zillion variables there. Agree with most all posted. _Assuming_ timing is somewhat close, it sure sounds like you have a lean condition. Since changing some items in the carb seemed to have some effect, keep working there. I'd get the stack of bowl gaskets and a selection of accelerator pump cams and squirters. Since lean is suspected, I'd go real big right off the bat and see what direction your problem goes in. 
Timing though, got to be sure of that. The "off the cuff" diagnosis is either timing or carb. You might be masking timing issues with the carb adjustments.


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## Cmeyer9424 (May 5, 2020)

Could y’all point me in the direction of the bowl and metering things I would need? I googled it but only see gaskets and not sure if that’s what I’m looking for.


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## BearGFR (Aug 25, 2008)

For example:
Gasket sets
The 'open' gaskets go between the fuel bowl and the metering block/plate. The others go between the metering block/plate and the carb body. These are for '4150' family carbs which I'm assuming you have, not Dominators.

If you're very careful you can often reuse the same gaskets multiple times. There's a torque spec for the bolts - around 15 inch pounds as I recall, but don't take my word for that without looking it up yourself.

When you remove the lower bolts, the fuel will drain out of the bowl(s) so the trick is to do that over some container to catch it, remove one of them, and drain the fuel before you continue. 

There are also nylon gasket seals under each bolt head that are easy to miss/lose if you don't know to look for and be careful with them. Sometimes they'll stay stuck to the fuel bowl when you remove the bowl screws then fall off later as work on the carb, then when you put it all back together and reinstall it, you'll have leaks.
Screw gaskets

Power valves will usually have a number stamped on them. That number is "inches of vacuum" below which the power valve will open and feed fuel into the power valve passages. If you have a power valve with too "high" of a rating in a carb on an engine with a rowdy cam and doesn't make much vacuum, then it may not make enough vacuum to keep the valve closed when it should be, and the car will run too rich at other than wide open throttle.
Many times only the primary side will have a power valve. There'll be a plug in the secondary side. One of the ways to test for a power valve problem is to plug to the primary side also, disable the secondaries completely (disconnect the linkage or disable the vacuum actuator if it has vacuum secondariesand block them closed) so that you can drive the car on the primary side only - see if that makes it act differently. It'll be down on power at full throttle because you won't have the secondaries to provide more air and fuel, but that can help you figure out the cause for problems that are happening at the various transition points (idle to cruise, low cruise to high cruise, cruise to wot, etc.)

Holley's have a reputation for being 'easy to tune' --- they aren't. What they are is easy to customize because so many of the parts can be changed (air bleeds, pump nozzles, pump cams, Idle feed restrictors (on some), emulsion well restrictors (on some), Idle bypass air (on some), power valve restrictors (on some) etc. etc. etc.) To take advantage of that you have to understand how they work, what your engine is telling you it needs, and what to fiddle with to deliver that. It's also easy to chase down the rabbit hole, making all kinds of changes without understanding completely what's happening, and just hoping to trip over something that works. 

Before I changed my car to a Holley format (actually an AED brand - 850 HO with annular boosters, mechanical secondaries, no choke horn, double pumps), I ran a real 455SD Qjet on it. My personal experience is that I found the QJet much easier to set up and get right, after I got Cliff's book and understood their systems. It was a big struggle for me to get that Holley 'right' everywhere: idle, low cruise, high cruise, launch, and WOT, even with the help of a quality wide-band digital air/fuel meter, Dave Vizard's book, and Tom Vaught's generous advise. The only problem I ever needed help on with the QJet was getting rid of a bog at launch, which turned out to have a cause not mentioned in any of the books or materials I had - fuel sloshing up through the secondary rod holes over into the secondaries and causing a momentary rich condition. I fought that one a good while until Cliff told me to try making a seal around the rods out of electrical tape.

I went to the Holley because I talked myself into believing that my engine needed "more" than what my QJet could deliver, otherwise I would have stayed with it. If I was wrong about that, I'm not sure I want to know... 

Bear


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## Mine'sa66 (Oct 30, 2019)

When I'm in Holley tune mode, I smear a super thin coating of Vaseline on my gaskets. Frustrating to repeatedly wreck them.
Don't over torque the screws! You'll mess up your bowls/power plates.


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## Lemans guy (Oct 14, 2014)

Bear and Mr. Taylor are both on it. 9 out of 10 carb problems are timing problems. You should always ensure timing is correct before carb tuning.

but since you are asking, Inthink you are lean going into WOT, that would be too small a stirrer and pump cam combo...

a stumble off idle is not usually the squirter from the acc pump, but the transfer slot in the side of the carb. If you have too much transfer slot exposed at idle, a common problem. Then you don’t get a smooth “transfer” from idle to off idle.

to fix that take carb off turn over and square the transfer slot hole try to set your idle mixture screws while either not disturbing that slot or only very minor changes...

WOT should also bring on secondary jets, as that circuit must be right as well...


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## Cmeyer9424 (May 5, 2020)

*update*

So I confirmed that the acc nozzle is a 31 size in the secondary but with the choke flap in the way I couldn’t manage to get the primary out to check it without fear of dropping it. I also reconfigured the throttle linkage and that greatly improved the off idle issue as well as transitioning to wot. Still seems sluggish but not much bog. I’m assuming this improved because of the slack in the cable was causing it to not get a clean crisp pull on the throttle. I did order a new throttle return spring since the one on it looks like an old screen door spring haha. I order it because when I would give it gas and let off it would raise the idle slightly even when I was off the glass but if I taped the pedal it returned to its normal ideal speed so I assumed the flimsy spring didn’t have enough to pull the linkage back fully. I got the one with the double spring setup, like one inside of the other. 

I’m really happy with this improvement, what would be a good direction to go next to hopefully improve the power I feel as if this motor should make? Any suggestions on timing changes? Initial is around 15 and with vacuum advance off and plugged looking like 30-32 at increased rpm. Should I maybe raise it a few degrees?


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## Lemans guy (Oct 14, 2014)

You should add the correct vacumn advance,...because you are giving up 10 more degrees of timing advance that you cannot get from the total mechanical advance.

racers take off the vac advance because they run at wide open throttle or on a drag strip,...light goes green pedal to floor..no need for vac advance if that is what you are doing.

But if it is a street car you are making it run hotter at idle and making it run poorly at most light throttle conditions because the timing as you are running it is tooretarded to burn those leaner mixtures.

if you are not just racing it put on a proper vac can... 10 more degrees at idle and light throttle will really help your engine run cool, smooth and powerful.

also it has no detrimental effect on top end as there is no vacumn at WOT so no Vcaumn timing...just your total mechanical which I recommend you start at 36 degrees....total and work from there.


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## CDub67 (Jun 20, 2019)

Hopefully this isn't too simplistic but I just added an M/E Wagner Performance adjustable PCV valve to my set up and it made a huge improvement. I've got an Olds 455 with a mild cam upgrade and Edelbrock Performer intake and carb. The power was pretty decent but it felt like it was restricted somehow. It would stumble at acceleration, had two small oil leaks I couldn't remedy, and had very strong emissions. I happened upon this product, read about others who had the same frustrations, and figured I'd give it a try. Really glad I did. Maybe it can help you, too. (I'm in no way affiliated with or compensated by them.) Good luck.


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> You should add the correct vacumn advance,...because you are giving up 10 more degrees of timing advance that you cannot get from the total mechanical advance.
> 
> racers take off the vac advance because they run at wide open throttle or on a drag strip,...light goes green pedal to floor..no need for vac advance if that is what you are doing.
> 
> ...


Just to make sure I understand correctly, I leave the vacuum hooked up to the distributor while I set total timing?


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## Cmeyer9424 (May 5, 2020)

CDub67 said:


> Hopefully this isn't too simplistic but I just added an M/E Wagner Performance adjustable PCV valve to my set up and it made a huge improvement. I've got an Olds 455 with a mild cam upgrade and Edelbrock Performer intake and carb. The power was pretty decent but it felt like it was restricted somehow. It would stumble at acceleration, had two small oil leaks I couldn't remedy, and had very strong emissions. I happened upon this product, read about others who had the same frustrations, and figured I'd give it a try. Really glad I did. Maybe it can help you, too. (I'm in no way affiliated with or compensated by them.) Good luck.


I’ll looks into this, thanks! Was it hard to setup or install?


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## CDub67 (Jun 20, 2019)

very easy


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## Lemans guy (Oct 14, 2014)

No, sorry Imwas not clear,...disconnect vac and plug to set base timing. Just make sure that the vac can you use pulls in the correct amount of timing, below your vacumn numbers.

some guys pull their cans out, you have not done that, but also some cans pull too much timing, and on today’s gas that does not help you run good.


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> Just to make sure I understand correctly, I leave the vacuum hooked up to the distributor while I set total timing?


No. Never set timing with the can connected. So many people get confused by this, probably because the word "total" implies "the sum of everything". 

However, when talking about setting ignition timing the word "total" means the sum of initial timing plus the maximum amount of mechanical timing in the system and does NOT include vacuum.

Here's the reason: Whenever you're adjusting timing, what you're doing is trying to optimize the amount of ignition timing for best performance under heavy load, like wide open throttle or pulling up a steep hill. Under those conditions, engines don't make any manifold vacuum to speak of, at least not enough to register on a gauge or to activate a vacuum advance canister. Whenever you're setting timing, you're adjusting for best power/heavy loads - where there isn't going to be any vacuum. You can't duplicate those conditions with the car sitting in neutral/park, so you set timing with the can disconnected. The only way you might be able to do it would be to do it while the car was strapped to a chassis dyno, pulling a load at WOT. Certainly not something I'd want to attempt, let me tell you.

The only time you would get the light out and use it with the can connected is if you want to MEASURE how much advance it's adding under various amounts of manifold vacuum, but you never SET timing with it connected.

Bear


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## Cmeyer9424 (May 5, 2020)

So how do you go about adjusting the vac can? Leave it plug up to vac and then use the timing light to see how much of a difference it makes at the higher rpm compared to the same rpm with the vac line off and plugged?


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## Lemans guy (Oct 14, 2014)

The easiest way is to read the number on the vac can, if it has one...some do some don’t it will have a number,....like 15 or 20. Some are marked for crankshaft degrees and some for distributors degrees,..which are Hal’s of crank. It does get confusing there, but a place to start.

If you are hooking to full manifold vacumn, which I recommend for the distributors that I curve,...some disconnect and plug dist vac and set base timing with your timing light and turning the dist by hand. Let’s say you want 10 BTDC, set it and lock it down at the dist.

Now just reconnect your vac advance and read the timing,...I set all vac cans for 10 degrees advance....so in this example you would have 20 BTDC showing on your timing light at idle.

the vac can is locked out at 10 it never goes higher, only lower as the throttle drops in this method.

Now if you hook to ported vac you will have to rev the engine and watch the timing light as the timing will start to advanceas the throttle plate barely opens...which allows vacumn to reach the port for the vac can....it will then add timing and then drop off as the throttle opens more.

ported vacumn is an emissions control method,nit runs the exhaust manifold real hot at idle and then burns off the noxious gas. It heats up your engine and makes your idle temps hot as a result.

there is no reason for it except emissions. If you need emissions put it there, if you don’t use full manifold vac.


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## Lemans guy (Oct 14, 2014)

Also know that many vac cans pull 20 and 25 degrees of timing at various load levels ...way to much causes poor running and detonation.

You have to put in the right vac can..that is what I am describing above......


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## BearGFR (Aug 25, 2008)

There is no "adjusting" the vacuum can, that is not unless you have an adjustable one - and most of them aren't. 

The ones I'm aware of that are are adjusted by removing the hose and inserting a hex key through the fitting and turning a screw. On those, you're adjusting how much advance the can is capable of adding under light load/part throttle conditions where manifold vacuum is high. 

The vacuum canister's purpose is to help a little with fuel economy and engine cooling. During conditions of light load/high vacuum, the fuel mixture will tend to be (notice I said tend to be, not will always be) a little leaner than during other conditions. Lean mixtures are a little harder to "light", take a little longer to burn completely, and tend to burn hotter than richer mixtures - so adding some ignition lead under those conditions helps to achieve closer to complete combustion (economy). For light load/part throttle you want 'enough' additional advance to compensate but not "so much" that you get detonation/pinging or surging. If you don't have 'enough' additional advance at part throttle/light load, then that air/fuel mixture is going to still be burning vigorously when the exhaust valve opens. That's going to heat up the valve, the exhaust ports in the heads, and the rest of the exhaust system more than if the mixture were to be completely combusted in the cylinder before opening the valve. It also means you're not getting the benefit of that combustion - you're wasting energy by sending 'fire' out the exhaust instead of using it to make cylinder pressure to move the car. 

So you set 'total' (total mechanical) timing for best power, then rely on the vacuum can to compensate and optimize light load/part throttle operation. If you have an adjustable can, the sweet spot is to set it so that you're "not quite" into the realm where you start to get surging/pinging/detonation during light load/part throttle operation - AFTER you've optimized total (mechanical) timing for best power.

Bear


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## Lemans guy (Oct 14, 2014)

Are you running an original points distributor or an HEI distributor?


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## RMTZ67 (Mar 12, 2011)

Probably best just to switch the can out. Lemans guy helped me out with a camaro I have . That can was pulling 20 so I purchased the can he recommended from Napa and that brought it down to 10 degrees. I switched it while the distributor was still on the car...took me all of five minutes.


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## Lemans guy (Oct 14, 2014)

Yeah RM it is worth the money, $15 and the effort 5 minutes to get that right....

most of the vac cans I see are pulling 20 to 25 degrees advance....just won’t make your engine run at peak efficiency


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## Lemans guy (Oct 14, 2014)

Excellent description bear, and I have a stack of adjustable vac cans in the cabinet under my two sun distributor machines. I always take them off. Now some do like them, that is OK.
I think maybe Big D uses one, but he is a racer and very knowledgeable about the nuances of his car, like you. You guys could optimize them.

But what I don’t like about them is that the Allen key in the stem adjusts the RATE of vacumn that the can pulls in....in other words at lower vac or higher vac. It does not change the total timing that the can pulls in. And most of them can pull like 25 degrees of timing.

Now Crane makes one with a stop limiter or you fabricate one and that will limit the total.

But, 10 degrees is optimal in addition to your 36 Total .......for 46..and that extra 10 is added to your base timing at idle that puts you in the perfect spot. Also since I recommend full manifold vac and most of the hot rods have somewhat lumpy cams there is almost always reduced idle vacumn and therefore can coming in low is better.

you must pull below your idle vac, and it’d that is already lowThat stock vac can will fluctuate in and out causing an erratic idle and drive one to drink.....

which maybe you should be doing anyway, being as we allneed to relax more


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> Are you running an original points distributor or an HEI distributor?


I’m running an HEI distributor which I just put a new MSD coil, ignition, rotor, and cap in. Would you suggest getting a new vac can to just add a fixed 10? I’m not sure if the one on there is adjustable or not but I personally don’t like a bunch of adjustments since it can lead to operators errors haha

could you possibly supply a pet number for it?

thanks for all the info guys, it’s been very informative!


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## Lemans guy (Oct 14, 2014)

Here is the one to get...All are made by the same manufacturer Standard Motor Parts, but different parts house put different numbers on them...

Standard Motor Parts ....SMP VC 302

Rock Auto calls it ..VC 302
O’Reilly sells it as ...BWD V482
NAPA sells it as....VC 1703

All will be stamped 626 10.........626 is an inventory manufacture number...The 10 denotes the number of timing degrees the can will advance at the crank.....10 degrees BTDC.

Specs it begins to move at 3 to 6 Hg......it will pull 5 degrees dist advance (which is 10 at the crank) at 7 to 9 hg.....many of our cars will run idle vac around 11 to 18 HG...with this can you can be assured that all 10 degrees of timing are in at those low vacs.....it drops out completely as you go to WOT.

I have tested a bunch of those cans on my distributor machines. They almost always pull 10, but a few pull 8 and a few pull 12 degrees. Sometimes I can loosen the screws on it and pull the can real tight against the front of the dist and get those2 degrees back. Or even a slight bend in the arm. But I am being way too exact....8 to 12 is perfect, and you will not need to adjust anything on it.

about 15 to $20 dollars.

Good luck and let us know how you do.


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## Cmeyer9424 (May 5, 2020)

Thanks for this! So once this is installed the initial timing I believe should be around 15 or so and total timing at increased rpm, with vac can off and line plugged, should be around 36? I think I read that in a earlier post.


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## Lemans guy (Oct 14, 2014)

The first number that you want to get once you put on the new curve kit weights is what is the centrifugal advance. That determines what your base timing will be. It is not an arbitrary number like 15 or 10. It is 36 -your centrifugal....so if your centrifugal is 24 then set your base at 12......if it is 22 then set your base at 14....always shooting for 36....

once the weights are on put on the two lightest springs for test, just so you don’t have to rev the engine too high.....then set base somewhere where it will start, 10 is good....now with your timing light or timing tape on the balancer rev up the engine Until the timing mark STOPS advancing. Note that number, then subtract your base timing in this example 10, and you will know your centrifugal total....It cannot go mechanically higher that that regardless of springs.

now set you base timingwith your new number vacum disconnected and plugged.

You can then try springs that bring that total in when you want. Try one lightand one medium spring. 3,000 is good even 3600. Then add on your vac can and you are set.

don’t stress about trying to get every last degree of timing in by 3000. Often 2 or 3 degrees linger out to 34 or 3600. It is a result of the springs. With that vac can attached do one last look at your idle timing, if your base was 10 you should have 20. That will run cool and strong.

Good luck and let us know how you do!


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## Lemans guy (Oct 14, 2014)

PS also google this article “ How to optimize timing in Pontiac engines”,.where you can do it on the bench with a protractor. I have 2 Sun distributors machines which is really easy to set me up. But you can do it without that.


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## Cmeyer9424 (May 5, 2020)

Just took it by a buddy’s shop and he suggested the same thing to change the springs in the distributor to green and also to change out the plugs.

Changing plugs was on my “to do” list. He suggested the Accel shorty plugs since the hooker headers make it impossible to get #8 out.

What plugs do y’all recommend since it does have a cam upgrade and other performance stuff.


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## Old Man Taylor (May 9, 2011)

I don't know what heads you have, but I've always run AC45RS in the 1960's heads that have been on my engines.


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## Cmeyer9424 (May 5, 2020)

Right now it has in it AcDelco R45TS


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## Old Man Taylor (May 9, 2011)

I think those are called the peanut plugs, but they're what I would run.


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## Lemans guy (Oct 14, 2014)

Those plugs are all good, sounds like you need the short one. Make sure your heat range on the plug is in the right zone. Too hot of a plug means the plug cannot dissipate heat into the head as well, too much heat causes pinging and detonation. So make sure you get it right for your engine. I run NGK plugs, ....R5670-6

Get Timing correct, right heat range plug, and fuel mixture right...(too lean runs hot causes detonation also and backfires..)

I like .35 gap...but you can go a little higher 40 even 45.....plug gaps are always working to get wider, not narrowing unless you have some major problems, normal wear widens the gap. If you start too wide and don’t keep an eye on em you with get hard starts and misfires.

I am not a fan of headers, because they often have these obstruction Problems. And put heat where you don’t want it. I run those big ram air exhaust manifolds, great flow and no maintenance issues.

But some guys love them and make them work....good luck!


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## Cmeyer9424 (May 5, 2020)

Little bit of an update today:

Ordered the vac can along with a set of springs. Should be here the middle of the week. Decided to pull the carb off and get some info on the nozzle and jet sizes.
Found out the primary nozzle is a 28 and secondary is a 31. Primary jet is a 71 and secondary is an 80. Also found out that in the primary acc pump cam it was installed in the bracket hole 1 but pump cam slot 2. So I moved it to cam slot one. Changed fuel filter, adjusted float level and acc pump springs. Took it for a test drive and could tell it made an improvement. 

It seems to me that the sizes of the nozzle or jets could be the issue with the stumble and backfire at wot but wanted to see what y’all thought.

Also got a video of it happening. First acceleration is rolling into the throttle. Seemed a bit sluggish but not bad. Second is from cruise idle to wot and that when it’s spits and sputters with a small backfire then takes off good.

Let me know if y’all are able to see and open the video.


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## Cmeyer9424 (May 5, 2020)

Here’s the link for the wot:
WOT

Here’s the one for rolling throttle:
Rolling


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## PontiacJim (Dec 29, 2012)

I can't help get the Holley adjusted as I am not a Holley guy, but yes, if the carb is too lean when you hit the accelerator, the engine just gulps in air and it can also backfire up and out the carb - stumbles.

I would keep working on the squirters, maybe the 50CC pump instead of the 30CC accelerator pump to fatten it up when you nail the gas. I think there is also a "cam" that can be adjusted?


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> Let me know if y’all are able to see and open the video.


I had to ' request access '.

Holley pump cams are color coded, with the color indicating how much volume they deliver, up to a point. What color plastic cam is on it now? There's also an adjustment for when the pump starts delivering fuel. You want it to start squirting immediately as soon as the throttle moves. If it's not adjusted right, then either there'll be a delay in actuating the pump (and you'll get a bog) or you won't get the full pump shot (too tight or too loose) or might even rupture the pump diaphragm by trying to push it too far (way too tight). Whenever the idle rpm is adjusted, also check the pump actuation. The change in the throttle linkage position due to changing idle also affects pump timing.

Try switching the pump nozzles, put the larger ones on the primaries. The larger nozzles allow the pump shot to be delivered sooner, smaller nozzles spread it out over a longer time. The pump cam combined with pump size (30 cc or 50 cc) control the total volume of the shot.

You can either make small incremental increases in delivery rate ( nozzle size ) and/or volume (cam and/or pump size) and "sneak up on it", or make a big, drastic change and work 'backwards', coming at it from the other direction.

If your problem is accelerator pump ( and it sounds like it is ) then main jet sizes in either primaries or secondaries won't affect it any.

Bear


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## Old Man Taylor (May 9, 2011)

You're going through a lot of the same stuff I went through with my Holley 780 vacuum secondary carb. I worked on it a long time before i went back to a tri-power. I had to work on the transition slots, the pump nozzle, the accelerator pump, the power valve and the vacuum secondary opening. The problem is that it's been so long that I don't remember the details accurately. I think I drilled out the nozzle to 0.036", I installed a 50 cc accelerator pump and I changed the pump cam. I think I used the brown one. I had to delay the opening of the secondaries,. but that's a problem that will be different on your carb. You have to make sure the transition slots are not exposed at idle, which means measuring them after you're happy with the idle. I don't remember the dimension, but I'm sure you can look it up in a book somewhere. Holley fixed these issues when they came out with the Dominator. It works well out of the box.


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## Cmeyer9424 (May 5, 2020)

I accepted the request. I’ll try and change it to public to make it easier. The cam is light pink with 3 options. I’ll switch the primary and secondary nozzle to see the change. The acc pump is a 30cc and I also checked the diaphragms to make sure they were good and they checked out.


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## Cmeyer9424 (May 5, 2020)

Would it be easier to just get a Edelbrock 750? I’ve had multiple people tell me to throw the Holley in the trash and get one of those instead.


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## Old Man Taylor (May 9, 2011)

I have no experience with the Edelbrock 750, but I've heard good things about it.


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## BearGFR (Aug 25, 2008)

No matter which carb you run, you'll find someone who'll tell you that it's garbage and others that will tell you it's the best there is. Let's see if you can get what you have sorted out before you start throwing money at another one. 

Here's the different pump cams:








And a chart that shows how they behave:









As you can see, the pink cam is one of the least aggressive. The yellow and brown are only for the 50cc pump which is why their curves are so different from the others. The orange, green, or blue would come on stronger and quicker than the pink one you have.

Do be sure to check the pump linkage adjustment so that it starts squirting the instant you touch the throttle. If it's not already set that way, that can make a big difference all by itself.

If moving the larger nozzles to the primary side makes it better, then you know it's wanting more fuel sooner. I'd be tempted to go to the orange cam and #32 or #33 nozzles on both ends in that case and see how it goes.

Transfer/transition slot adjustment. Look at the carb from the underneath side. The transfer slot openings should look like squares whenever the throttles are closed in the idle position. If they're "taller" than they are "wide", there's a good chance that you're already feeding fuel from them at idle such that there isn't "enough" transfer slot left to smooth the transition from idle to cruise - which is what they're there for. I don't recall you mentioning whether or not your carb has 4-corner idle? If it does, then the way to get both your transfer slot opening and the idle rpm to play nice with each other is to set the primary throttle opening such that the transfer slot openings are "correct" (square shaped) and then use the secondary idle speed adjustment to set idle rpm. There are transfer slots on the secondaries too if your carb has 4-corner idle, but since the secondaries don't open until you're deep into the primaries, they don't have as much an effect on the transition phase as the primary side does. 

You may have been told to never fiddle with the secondary idle speed and that's -generally- true unless you've got a good reason to do it, which this would be.

Some Holley's have and adjustment for idle bypass air. If yours does, it'll be a screw that you can get to underneath the air cleaner stud once you remove that. That's another mechanism you can use to get your idle mixture and rpm "right" without having to open up the primary slots too much. That can be needed in cases where you've got a relatively rowdy cam that would otherwise need a lot of throttle opening to get it to idle (thus exposing too much of the slots). You may have seen cases where folks have drilled small holes in the throttle plates. That's another way to get more idle air on carbs that don't have the adjustment for it, and don't have 4-corner idle. That's kind of a 'last resort' move though because if you get them too big, it's pretty tough to make them smaller again 

Bear

If moving the larger nozzles to the primary side makes it better


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## Cmeyer9424 (May 5, 2020)

Those charts were really informative! Were you able to open the links to the videos? I’ll swap the nozzles tomorrow and update to what happens. It is a four corner system and when I had the carb off today I did turn it over and adjust the idle screw to make it a the opening more square. I believe it was quite larger and more rectangular at first.

Based on the chart I wouldn’t mind upgrading to a 50cc and using a blue or yellow cam!!

When upgrading the cam on a double pumper you upgrade both primary and secondary correct? Same as if you were to upgrade to a 50cc pump I would need one for the front and one for the rear of the carb


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## BearGFR (Aug 25, 2008)

The trick is finding what your engine likes. There's no one "best" or "right". The pumps don't have to be the same on both ends. The key is finding what combination gives your engine enough fuel so that it doesn't stumble, but not so much that you create another one. You'll get a bog from too much fuel also but it'll behave differently. It'll seem to "go" for a fraction of a second, then fall on its face.

Now, I'm running a 461 with a moderately rowdy solid roller, so my setup is different from yours. My carb came with a 30cc front, 50cc rear pump. I think it had the pink cam on the front, brown cam on the rear and #35 nozzles on both ends. I had a stumble when I hammered it, so I started trying to go gradually bigger. It was getting slowly better but only slightly, so I went "the other way" and went way overboard on both ends, thinking that I'd end up having to pull things back to arrive at the best combination. To my surprise "way overboard" was exactly what it seemed to like, so I left it that way.

I've heard of people running the big pump on the front and the small pump on the rear too. The key is paying attention to what your engine is telling you it wants, then doing that.

Oh, and it still tells me I don't have access to the videos.


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## Cmeyer9424 (May 5, 2020)

I just made them public where it says anyone with the link can view them so hopefully that will allow y’all to view them. I’m gonna swap the nozzle and go from there.


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## Cmeyer9424 (May 5, 2020)

What did you end up using for the “way overboard” combination? Just curious on how much of a change you’re meaning


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> What did you end up using for the “way overboard” combination? Just curious on how much of a change you’re meaning


Well, I hesitate to say because you might be tempted...  I went to the max - 50cc pumps on both ends and yellow cams shooting through #46 nozzles. I had gotten tired of trying to ease into the right combination and decided to make a drastic change to make something happen. I really expected it to create a super rich bog and was stunned when it didn't. I might could pull it back from that some, but it doesn't bog at all. I run drag radials on the car full time, but on the black top road in front of our place if I hammer it from a stop it spins all the way through first and second gear, and doesn't hook until it hits 3rd. 

Right now I'm waiting on the machine shop to finish work on my block (long and somewhat sad story involving a previous machine shop), then I'll be looking at an 8 week wait to get a set of pistons, then waiting again for a re-balance before I can put it all back together and get it into the car.


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## Cmeyer9424 (May 5, 2020)

Yeah the old hurry up and wait...never fun. You’re right, I am tempted ....but I’ll try and make small changes first before I throw it all at it!


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## Cmeyer9424 (May 5, 2020)

Swapped the primary and secondary nozzles and it seemed to like it I believe. No from cruise to wot it just stumbles but no backfire and when it goes it goes! I’m think maybe a .35 nozzle in both? Kinda the same thinking go big as big as the 30cc will allow and then either go bigger or tune down. Also will see about the orange pump cam before going bigger than a .35


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## BearGFR (Aug 25, 2008)

FYI, Amazon has lots of different size pump nozzles available, also cams, air bleeds, jets, etc. if you want to start building an inventory of parts to tune with. There's also a Holley part that makes adjusting idle speed on the secondary side a lot easier. Holley part# is 26-137 also on Amazon. Kinda pricey in my opinion, but if you need to make that adjustment and get tired of having to remove the carb to do it, they come in really handy.
There's a lot of good information over on PY, and there are books - like the one from Dave Vizard.

Bear


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## Old Man Taylor (May 9, 2011)

You are fighting exactly what I was fighting in your WOT video. I got it to where the main issue was shifting gears. I would hesitate as I hit the gas on each gear change. I would start right out with the 50 cc pumps and 35 or 36 squirters and go from there.


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## Cmeyer9424 (May 5, 2020)

I’ve got some 35 nozzles coming. Should be here middle next week.


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## Cmeyer9424 (May 5, 2020)

Got the 35 nozzles installed and not really a difference. I have new plugs coming as well as 50cc conversion kit for the primary and secondary. What nozzle and pump cam did you end up running to fix your problem?


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## Lemans guy (Oct 14, 2014)

Agree with Mr. Taylor, I only have one acc pump, vac secondaries, but I use 50cc and 41 squirter....no bogs and right AFR...


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## Cmeyer9424 (May 5, 2020)

*update*
got the new vac can on and got the timing set to 36 total. The car made an improvement just from this alone. Next I put in the new 50cc accelerator pump and the brown pump cam. No more stumble at wide open!! I have the other 50cc upgrade to install on the secondary and will update from there.

I will say now that I have the stumble issue figured out id like to get more power and was wondering what y’all would suggest as a good next improvement? It’s power is decent now but doesn’t really have that muscle car power that I feels like it should haha.


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## Lemans guy (Oct 14, 2014)

Set your timing curve, to have centrifugal come in early, and make sure your vac can pulls only 10 degrees of timing,.....I recommend a good PCV system, ME Wagner is the best..

And you can use an AFR meter to set your fuel curve, these are small things,...big changes may require , engine , trans or rear end gearing changes...

but first get what you got to peak and then see....


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## Cmeyer9424 (May 5, 2020)

Timing curve is set with the springs correct? I have a set of them but didn’t know exactly how to change them out or which ones to go with.


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## Lemans guy (Oct 14, 2014)

Yes read a few of the forum discussions on setting timing....if you know for sure that you have 36 total.....then you are in a good spot to move forward....some claim they have 36.....total but actually have more at a higher RPM....that is not total....total means it can never go higher at 4000, 5000, or higher RPm.....

once that and vac can are right you can experiment with the springs to see at what RPM you can bring that all in.

Try a light and a medium spring from the kit...

should get you close, then use your timing light or timing tape on the balancer to see when that 36 comes in...disconnect and plug vac for that test....

centrifugal timing is RPM dependent only


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## Cmeyer9424 (May 5, 2020)

Right now, I plugged the new vac can and had a buddy increase rpm till it stopped advancing with the timing light. Then dialed it back till the timing light read 36 with the balancer mark lined up to 0. I had a cheap tach installed and didn’t trust it. I’m going to install an Autometer one and then mess with the springs. 

The new vac can you gave me the model number for doesn’t need to be adjusted does it? Just pull the old one out and install the new one correct?


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> Timing curve is set with the springs correct? I have a set of them but didn’t know exactly how to change them out or which ones to go with.


Lighter springs and/or heavier weights will make the advance "come in" sooner/quicker. Heavier springs/lighter weights do the opposite. On factory distributors and HEI's, the springs and weights are located underneath the rotor. 

If you've gotten rid of the bog, changing the curve is not going to make a big difference - not enough for you to feel in the seat of your pants, but maybe enough to show SLIGHTLY on an accurate set of timing clocks at the drag strip.

If the bog is completely gone (no hesitation at all when you hammer it from an idle at standstill) then there's no reason to put on the 'other' 50 cc pump. "Too much" shot will also create a bog.

If'n it were me, my next move would be to add a GOOD air/fuel ratio meter so you can make sure the mixture is right in all modes of operation: idle, low cruise, highway cruise, wide open throttle. 

There are both hand-held ones (Innovate LM-2 for example) and permanently installed ones (I have an AEM X-series in my '69) available. All require a fitting to be welded into an exhaust pipe near the engine to install an oxygen sensor. 

This is the one I have in my car:
AEM Electronics X-Series Wideband UEGO Air/Fuel Sensor Controller Gauges 30-0300

Bear


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## Cmeyer9424 (May 5, 2020)

I installed the other 50cc this morning and I hammered on it and there was an ever so slight bog. I can’t say for sure if it was there with or without the secondary 50cc installed.

I currently have .35 nozzles in both, since I now have the bigger pumps, should I increase nozzle size and if the bog increases I’ll know it’s too rich?

I looked into ordered an AFR gauge and dang those thangs are pricey for a gauge ha!


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## Cmeyer9424 (May 5, 2020)

Also, do y’all have an experience in the difference between the brown pump cam and the yellow? I know by the chart the yellow seems more aggressive but wanted to know if anyone had first hand experience.


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> I installed the other 50cc this morning and I hammered on it and there was an ever so slight bog. I can’t say for sure if it was there with or without the secondary 50cc installed.
> 
> I currently have .35 nozzles in both, since I now have the bigger pumps, should I increase nozzle size and if the bog increases I’ll know it’s too rich?
> 
> I looked into ordered an AFR gauge and dang those thangs are pricey for a gauge ha!


Did you try hammering it without that second 50cc pump?


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## Cmeyer9424 (May 5, 2020)

I did, I just can’t say for exact certainty that it had a bog. The bog with both 50cc installed was pretty small so I may not even have noticed before. I think it may need a .37 or .41 but I can always pull the 50cc back off and put the 30cc on and go hammer on it to be certain


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## BearGFR (Aug 25, 2008)

Here's another way to tell which direction it needs to go: If the bog is "instant" -- meaning that it happens just as soon as you crack the throttle, then it's probably lean -- meaning that it wants more fuel sooner. If it feels like it "goes" for just a very short time and THEN falls on its face, then it's rich and you should take some shot out of it -- less aggressive cam, smaller nozzles, etc.

Pump size combined with much "lift/travel" is in the pump cam determines the total volume of fuel that gets delivered. Nozzle size and also the shape of the pump cam (how 'steep' the ramp is) determines how long it takes for the shot to be delivered.


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## Cmeyer9424 (May 5, 2020)

Good to know! I’ll get it out this evening and confirm if it’s instantly or not. Thanks!


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## Lemans guy (Oct 14, 2014)

Your vac can needs no adjustment if it is the one I told you to get for an HEI distributor. Just hook to full manifold vac and go.

Sounds like you have established your 36 total....now with vac unplugged where is your base timing? If it is ten then you know that your have 26 degrees of centrifugal advance.

you can then reconnect the vac and shoot the timing light to get your idle timing....if your base was 10...and now you added 10 vac....you will see 29 or so on your timing light.

Make note of your numbers for future ref...

then change those springs and see-when the curve comes in again with your timing light.

You can get them down to 2500, but those will be light springs and sometimes bring in timing on top of your idle....

3000 RPM, 3200, even 3400 will run very strong...


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## Cmeyer9424 (May 5, 2020)

When I check base timing and idle timing the car is at idle correct? Also, when checking idle timing do I do the same thing and dial the timing light till the mark on the dampener lines up with zero but this time at idle?
I just wanna make sure I don’t need to call my buddy again to raise the rpm haha


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## Lemans guy (Oct 14, 2014)

Yes correct, it will just show you what your idle timing is with the vac advance hooked up....what was your base timing, vac plugged At idle?


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## Cmeyer9424 (May 5, 2020)

So I checked the timing at idle with the vac line off and plugged and was able to get a picture of it’s position. But I think I’m doing something wrong because with or without it plug nothing changed...

I went out and hammer on it good and it does still instantly bog just a bit. Definitely improved but still hesitates.What size should I go? I’m honestly thinking a 41 or 45. 

I’ll attach the picture of the timing mark. I was able to get the picture using the burst photo feature and picked the one where it was visible.


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## Lemans guy (Oct 14, 2014)

Just up the squirter some 38 maybe, just trial and error to lose the bog ....

make sure that your vacumn is not hooked to ported vacumn. Ported vacumn pulls no vacumn at idle...put your finger over the vac hose...is it pulling at idle? If not you need to go to a different vac source


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## Cmeyer9424 (May 5, 2020)

I believe it is hooked to ported and my trans vac line is hooked to manifold. I’ll switch them and check it again. Thanks!


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## BearGFR (Aug 25, 2008)

You'll find folks who argue passionately both ways on vacuum source for the advance mechanism, either ported or unported. My opinion is try both, use whichever one your engine seems to like the best.

If you've got "insta-bog" but it's not severe (sounds like it's not) - then make small changes - like in 10% increments - until you find the happy place. Also, make sure that there's no "slack" in the pump linkage and that it hasn't already "used up" any pump travel at idle.
There's a video here:
How To Adjust The Accelerator Pump Arm on a Holley Carburetor - Holley Blog
To summarize though, you're trying to accomplish these things:

Make sure that the pump is completely "relaxed" when the throttle is at idle, and
The pump starts to squirt with even the tiniest/slightest movement of the throttle - no slack whatsoever, and
At full stroke, the pump arm isn't moved so much that there's a risk of tearing the pump diaphragm

Bear


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## Cmeyer9424 (May 5, 2020)

BearGFR said:


> You'll find folks who argue passionately both ways on vacuum source for the advance mechanism, either ported or unported. My opinion is try both, use whichever one your engine seems to like the best.
> 
> If you've got "insta-bog" but it's not severe (sounds like it's not) - then make small changes - like in 10% increments - until you find the happy place. Also, make sure that there's no "slack" in the pump linkage and that it hasn't already "used up" any pump travel at idle.
> There's a video here:
> ...


Thanks for the video link! A lot better than the one I found haha


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## Cmeyer9424 (May 5, 2020)

*Update*
So I tried bigger nozzles with no luck. Ended up finding the configuration that seems to work the best. 
50cc pump on the primary and a 30cc on the secondary with .35 nozzles in both.Once I get the AFR gaugeI I can fine tune it some more. Thank y’all for all the help!!


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## Lemans guy (Oct 14, 2014)

Good work C, you stayed with it.....with that AFR gauge you can tune it in nicely.....

I like 13.8 for idle, 13.2 for light cruising, 12.2 for power,......when Accelerator pump is on,...

Or Power valve deployed or secondaries on.....12.2........I have found this runs nice and not too lean or rich. You do get slight variations on AFR with the seasons temp changes and this allows a nice ride in all weather and good power.

Computers and sophisticated FI can maintain Stoicometrixpc,..14.7 for pure gas ..14.1 for 10% ethanol gas,..but a carb cannot,..and too lean will make it run hot and too rich will wash down the cylinders and some and burn fuel.....

Good work!


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> Good work C, you stayed with it.....with that AFR gauge you can tune it in nicely.....
> 
> I like 13.8 for idle, 13.2 for light cruising, 12.2 for power,......when Accelerator pump is on,...
> 
> ...


Im back at it with trying to fine tune the carb/engine since the weather is nice again. Got it back out and for some strange reason the lean bog is back. Could be me only running 93 gas and need to adjust the AF screws or something.

I can’t remember if someone mentioned this, but once I make an adjustment can I just snap the throttle at the carb with the car in park to test if the bog is gone or does the car need to be under load?


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## Lemans guy (Oct 14, 2014)

Usually you need the load.... but you can try it to see..


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## Cmeyer9424 (May 5, 2020)

I’ll give it a try and update on here


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## Cmeyer9424 (May 5, 2020)

Did a lot of tuning today and finally got the bog a 100% out! I think the whole problem was with the secondary pump arm/cam. I noticed when the throttle rotated enough for the secondaries to open, the nozzle didn’t spray for a second or two. I adjusted the screw/spring thing and reconfigured the pump camp and now it’s all good!
I went through and adjusted the idle and the mixture screws so it’s happy together as well. 

I do have a few question that came up through my test drives 

1. Have y’all ever encounter and issue where you go to brake, harder than just easing to a stop, and the car wants to die? I’ve felt like it wants to so I pushed down on the brake a good bit today and sure enough it sputters and dies.

2. Is it normal, with an upgraded cam, to see the oil pressure gauge slightly move up and down when in gear while on the brake? Not as noticeable when in park or neutral. It was more noticeable before I adjusted the idle and mixture screws.

3. How do I go about hooking up the downshift solenoid? I believe in another thread about a wiring issue I had, a member told me that one of the unplugged wires under the hood was for this. I think this will greatly help when I got to WOT while cruising around. It just needs that get up and go haha.

4. If I adjust timing do I need to adjust the idle and mixture screws again or since I have them set are they good?

Thanks for any input!


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## Lemans guy (Oct 14, 2014)

1) you will have to gently adjust your idle mixture and throttle plate to prevent that stall. You have seen the discussions on here about the anti-stall dashpot. They were on many cars and what they did was just let the throttle plate not slam shut, they dampened the closing of the throttle plate to prevent that stall. On a fast brake when the throttle slams shut you spike lean and get a stall. So opening the throttle screw a tad more , not much and closing the mixture a tad. Working it back and forth. A small change to find the sweet spot. Using an AFR meter makes it much easier as this is fine tuning the carb.

2) Not sure that it is bad if it moves a bit, as long as the pressures are strong.

3) If there is a lockdown we’re for whatever trans you have yes hook it up. I have a th350 so it is a wire cable.

4) Timing should be set first, then carb adjustments. After that looks good you should go back and check timing. But often no change is needed. For example, RPM’s and vacumn effect timing, so if you changed them enough you need to go back and check. But if the changes were slight it may have no effect.


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## Lemans guy (Oct 14, 2014)

“Kick down”....the spell correct changed it to “lockdown”.....sorry.


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> “Kick down”....the spell correct changed it to “lockdown”.....sorry.


I have the th400 I believe


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## Cmeyer9424 (May 5, 2020)

So I’ve been diving into this downshift linkage and boy did it snowball! So the throttle cable was to short so I relined it and finally got the top of the pedal to come into contact with the downshift switch and make it properly move. I’ve come to notice that when the pedal is pushed to the floor the carb linkage goes about mid way, maybe a bit more but if I work it with my hand I can make the throttle go till it stops fully. Should I be able to make the throttle linkage on the carb go to full lock with the gas pedal or is it only supposed to go maybe 1/2 to 3/4 of full lock?

Also, how do you properly attach a stock throttle cable to a Holley 750 double pumper? Right now it’s cobbled together


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## Cmeyer9424 (May 5, 2020)

I ended up buying an adjustable aftermarket pedal and a universal throttle cable kit. Got it installed and now have full throttle! I also noticed my carb gasket was a bit worn out and thought that might be causing a vacuum leak. I put a new one on and vacuum gauged reads right under 15 steady where before it was around 10-12 and would be jumpy. 

But now it seems to ideal kinda high, when I put it in reverse it kinda jumps/loads up. The ideal screw won’t ideal it down anymore and if I turn the mixture screws in it ends of running rough and then dies. What could cause this?


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## Lemans guy (Oct 14, 2014)

If your throttle screw is open too much past the transfer slot the mixture screws won’t work good or at all. They are working some as they stalled it but maybe not enough.

best is to square the transfer slot by taking carb off and then start mixture screws at thebeginning and reset


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> If your throttle screw is open too much past the transfer slot the mixture screws won’t work good or at all. They are working some as they stalled it but maybe not enough.
> 
> best is to square the transfer slot by taking carb off and then start mixture screws at thebeginning and reset


I checked the primary transfer slot and it was a square and I noticed the secondary wasn’t showing at all so I made it a square too. Is this correct?


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## Lemans guy (Oct 14, 2014)

Yes they should be the same as the carb idles off all four circuits. Adjust all four idle mixture screws the same


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## Cmeyer9424 (May 5, 2020)

I checked those today as well. So both transfer slots match and all four idle mixture screws match. It’s like the idle set screw backs out and the throttle linkage can go back anymore to lower the idle so the screw just unscrews


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## Lemans guy (Oct 14, 2014)

Very small movements of the four mixture screws together may be needed. Those quarter and half turns are sometimes too much. Go small, turn each mixture screw in 1/8 of a turn and let it reset. You may have to even slightly close the transfer slot. A square is beat, but if you cannot get it right a very slight move May help.

make a mark to see where they are square and then you can make a slight move. I would slightly close the mixture screws to see if I could get the idle down a few times fires. And make doubly sure that your fast idle cam on the choke side is not hanging your throttle up andslightly more open.

also do all adjustments except choke fully warmed up.


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## Cmeyer9424 (May 5, 2020)

Does a manual choke have a fast idle cam?


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## Lemans guy (Oct 14, 2014)

No, that is just the cable. But make sure your choke plate fully opens, if not it will up the idle. Or if the cable slips back. When fully opened it should be vertical.

also as you are adjusting mixture you may have to close the rear transfer slot again. The fron one is the crucial transition. The back one not so much. You just have to try and see.

I would try all four mixtures than close up secondary transfer slot trying to leave front one square...and see where you can achieve idle


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## Lemans guy (Oct 14, 2014)

750 or 850 with hotter cams is ok....if everything is not factory don’t try for 600 or whatever, different carbs, timing , cams all change those things plus today’s gas is different as well


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## BearGFR (Aug 25, 2008)

Cmeyer9424 said:


> So I’ve been diving into this downshift linkage and boy did it snowball! So the throttle cable was to short so I relined it and finally got the top of the pedal to come into contact with the downshift switch and make it properly move. I’ve come to notice that when the pedal is pushed to the floor the carb linkage goes about mid way, maybe a bit more but if I work it with my hand I can make the throttle go till it stops fully. Should I be able to make the throttle linkage on the carb go to full lock with the gas pedal or is it only supposed to go maybe 1/2 to 3/4 of full lock?
> 
> Also, how do you properly attach a stock throttle cable to a Holley 750 double pumper? Right now it’s cobbled together


Here's how I did mine. I used a socket head stainless screw the same size as the hole in the end of the throttle cable, drilled a hole and mounted it to the throttle arm, and use a nylon lock nut to hold the cable on between two washers. 

















Bear


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## Cmeyer9424 (May 5, 2020)

I adjusted the transfer slots, messed with the mixture screws, and idle screw got it where I like it but when I give it some gas the idle comes up. It’s like the springs aren’t pulling it back enough. I can manual push the linkage closed more to lower the idle


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## Lemans guy (Oct 14, 2014)

Maybe your springs are too weak...


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## Cmeyer9424 (May 5, 2020)

Lemans guy said:


> Maybe your springs are too weak...


Haha my exact thoughts but if I keep adding more springs then it’s too hard to push. I kept messing with it and took it up to a speed shop that friend recommended. Awesome place and people. We checked the timing and other things. It’s running good now. 38 total timing and checked over the carb setup.


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## Lemans guy (Oct 14, 2014)

Good,...those strong springs will give you a workout and you won’t have to buy one of those home gym spring loaded thing-a-bobs.

just go for a cruise!


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