# 64 GTO 389 Tripower acceleration



## Rlamarche1 (Nov 22, 2016)

The car runs great until I have run it for about an hour and is @ 180 degrees. After shutting down and restarting a while later it wants to sputter when accelerating in first gear. Does anyone have any suggestions?


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## PontiacJim (Dec 29, 2012)

Rlamarche1 said:


> The car runs great until I have run it for about an hour and is @ 180 degrees. After shutting down and restarting a while later it wants to sputter when accelerating in first gear. Does anyone have any suggestions?


Heat soak? Ethanol fuel boiling either in the carb or somewhere along the fuel line - filter, pump, steel line along the engine. That would be my first guess.


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## Rlamarche1 (Nov 22, 2016)

I was afraid you were going to say that Pontiac Jim. I run 93 octane non-ethanol gas, but from what I have read, heat soak can be a problem with carbureted engines in hot weather. I guess I'll just have to live with it.
Thanks for the response!


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## PontiacJim (Dec 29, 2012)

Rlamarche1 said:


> I was afraid you were going to say that Pontiac Jim. I run 93 octane non-ethanol gas, but from what I have read, heat soak can be a problem with carbureted engines in hot weather. I guess I'll just have to live with it.
> Thanks for the response!


Not saying I am 100% right, just my best guess from your description and your location. The true test will be when your temps get a little cooler outside. If the problem goes away, then you know exactly what it is. It could be "other," but if the car runs fine otherwise, that is what I would look into.

My brother has had the same symptoms/issues with his '57 Caddy and '73 RoadRunner with 360/Six Pack. Heat soak on hot days in the 90's was a problem when the cars were shut off and then restarted shortly thereafter, like getting gas.

He installed an external electric fuel pump near the gas tank that pushes the fuel to the factory fuel pump on the '73. He said made a world of difference when he now starts it - fires right up after shutting down. So he did the same to the Caddy and he said it too helped with the hot re-start problem.

I am convinced that an electric fuel pump is the way to go in helping the hot re-start problem. I plan on adding an electric fuel pump, pressure regulator, and 1/4" return line to ward off the problem, ethanol gas or not. Of course phenolic spacers under the carbs could help a little and these are available for the tri-power. Blocking off the exhaust heat crossover on the intake that goes under the carb is also another option. Seeing your location, you probably won't have too many cold days where this could be a problem. The A/C cars had a 1/4 return line which can also help if you do not have this and wanted to add it. 

I get these clips/stories from Speedway Motors- which I buy parts from for my projects. This episode is on the fuel system for their project Chevelle. I like what they did and these systems are becoming more reasonable to purchase. You can do the in-tank system or add an external electric pump and the pressure regulator with or without the factory fue l pump. At the bottom of the page you can click on the components to learn more. https://www.speedwaymotors.com/the-...&utm_campaign=chevelle101518&utm_content=hero


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## Rlamarche1 (Nov 22, 2016)

Before I do anything, I am going to do as you suggest. It is starting to cool off a little bit. I'll see how it does when the temps are cooler. I never have a problem restarting. It always starts up immediately first crank. It is on initial acceleration in first gear when it sputters. Again, thanks for the input.


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## My65goat (Jul 26, 2017)

Rlamarche1 said:


> Before I do anything, I am going to do as you suggest. It is starting to cool off a little bit. I'll see how it does when the temps are cooler. I never have a problem restarting. It always starts up immediately first crank. It is on initial acceleration in first gear when it sputters. Again, thanks for the input.


Just a thought. ...are you running a points distributor? Maybe it is a coil or points issue? The reason I say this is because you stated that it starts right up on first crank when hot. That leads me to believe that it may not be a fuel problem. Just a thought. ....


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## Rlamarche1 (Nov 22, 2016)

Yes I am running a points distributor. The coil/points issue is certainly something to be considered. Thanks!


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## PontiacJim (Dec 29, 2012)

Rlamarche1 said:


> Before I do anything, I am going to do as you suggest. It is starting to cool off a little bit. I'll see how it does when the temps are cooler. I never have a problem restarting. It always starts up immediately first crank. It is on initial acceleration in first gear when it sputters. Again, thanks for the input.


I am still leaning towards "heat soak" and the crappy gas we have today, so I would see if cooler outside temps cure the problem. But, it could still be something else if you want to explore further.

It could also be the accelerator pump in the carb worn out or going bad. It is not giving th carb a good "squirt" of gas when you first open up the carb on acceleration. 

The carb opens up and engine vacuum drops creating a lean condition and the extra shot of gas from the accelerator pump feeds the engine through this momentary low vacuum condition to richen up the air/fuel mixture so the engine does not stumble and picks up as intake velocity increases to pull fuel through the carbs venturies.

However, if this were the problem, you would experience this under all hard acceleration conditions, not just first gear.

It could be an electrical problem as My65Goat has suggested - weak coil, point gap needs to be verified, points may need replacing, or might need a tune-up if this has not been done in a while.

Your vacuum advance/timing could also be suspect. If the vacuum advance is not operating correctly this could be giving you a problem. When the car is running, it is at its highest vacuum point and vacuum advance at full operation. Once you accelerate hard, vacuum advance is eliminated and the engine operates on mechanical advance - initial advance at the crank and mechanical advance through the weights in the distributor. If this is not adjusted correctly, to include your advance curve in the distributor, it could cause the same effect as you are experiencing on 1st gear acceleration only. Once rolling and the engine in higher RPM's in other gears, you may not experience this hesitation due to the higher range of the RPM's. So it is important to know intial timing at the balancer, how much/maximum mechanical advance the distributor provides and at what RPM that is, how much vacuum advance your vacuum can provides, what your total mechanical advance (initial + distributor) and at what RPM this is reached, and then what your total mechanical plus vacuum advance is. All these specifications will dial-in your timing and the advance curve of the engine. So, that stumble could be caused by a timing issue.

I might simply advance the distributor a few degrees to see if the stumble improves or goes away. CAUTION! If in advancing the timing for this test you hear any kind of engine "pinging" or "rattling" from detonation, take your foot off the gas pedal - your timing is too far advanced and you do not want to damage the engine. If it does improve your problem, return the distributor back to its original setting so as not to have timing too far advanced and then go about tailoring your engine timing to bring it to where the engine likes it, not what the owners manuals say to do. Just a couple of advance degrees at the crank pulley can make a big difference in engine performance.

So a few things to look into and check. To know what it is, sometimes you have to check/adjust things to know what it isn't. :thumbsup:


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## Rlamarche1 (Nov 22, 2016)

I to am leaning towards heat soak, however, I will look into other scenarios as you suggest. Right now timing is set to 6 degrees btdc and points gap @.018. I am still going to wait for cooler temps. Highs this week in the low 70s and lows around 60.
I look at the forum quite frequently and I as well as other members, I am sure, appreciate the time and effort you spend to help others out and share your knowledge. It doesn't go unnoticed!


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## geeteeohguy (Feb 2, 2008)

I'm with Pontiac Jim 100% on this---it was my first thought too. I have experienced this with several carbureted cars, the worst one is my '61 Corvette with dual 4 barrel carbs. It actually will die out after a ten minute heat soak...as soon as I drive a block or two to pull cool air though the radiator, it does just fine. An electronic HEI ignition is MUCH more likely to give you heat related issues than a standard points and condenser ignition system. I used to tune cars for a living, and worked on literally thousands of carbureted cars with points ignition. This problem with heat soak didn't occur until about 15 years ago as fuels were being formulated more for FI cars and are more volatile than the old fuels, which resisted boil-off.


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## Rlamarche1 (Nov 22, 2016)

Thanks Geeteeohguy. The easiest thing for me to do right now is see how it does as the temps cool here, That way I can try to eliminate the heat soak issue. If it is a heat soak issue, I think the first thing I will try is the electric fuel pump from the gas tank going to the manual fuel pump and see if that helps.


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## cij911 (Oct 25, 2017)

Rlamarche1 said:


> The car runs great until I have run it for about an hour and is @ 180 degrees. After shutting down and restarting a while later it wants to sputter when accelerating in first gear. Does anyone have any suggestions?


I do NOT think this is a heat soak issue.

You state the problem only happens in first gear? Are you logging or monitoring your AFRs? Is this with just the primary carb or the outer two engaged as well? (For example if you accelerate gently does it sputter? Or does it only happen when you nail it?)

Is this a manual or automatic? And this doesn't happen in 2nd - 4th gear?

What type of choke are you using (the factory setup or did you convert to electrical)?

Have you looked at your plugs? (I'm guessing you are running very rich.)


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## Rlamarche1 (Nov 22, 2016)

Don't mean to sound stupid, but what are AFR's? Just with primary carb. Manual M20 4 speed. Doesn't happen in any gear but first with mild acceleration, not engaging outer carbs. When I nail it everything is fine. Factory setup with choke stove. Haven't checked the plugs.


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## PontiacJim (Dec 29, 2012)

Rlamarche1 said:


> Don't mean to sound stupid, but what are AFR's? Just with primary carb. Manual M20 4 speed. Doesn't happen in any gear but first with mild acceleration, not engaging outer carbs. When I nail it everything is fine. Factory setup with choke stove. Haven't checked the plugs.


AFR is referencing Air/Fuel Ratio They make an AFR monitor/gauge that you can add onto any car just like an aftermarket oil pressure or temp gauge. It allows you to watch the AFR of your system and allow you to see how any of your adjustments change the AFR - lean or rich. Modern day electronics and just another gadget to constantly watch to make you nervous or frustrated as you drive down the road and it changes AFR measurements on you when you get crappy gas, air filter gets clogged, fuel pump is getting weak, fuel filter is plugging up, carb is messing up, spark plugs are getting dirty or fouled, ignition problems, outside air temp & humidity changes, you accelerate, you decelerate, your cruising, you make a hard corner and the gas in the bowl sloshes..........you know, those kind of things. 

Why enjoy your car and take in the scenery not knowing what the AFR is when you can focus on the gauge and be a bundle of nerves thinking something must be wrong everytime it fluctuates. :thumbsup:


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## cij911 (Oct 25, 2017)

Rlamarche1 said:


> Don't mean to sound stupid, but what are AFR's? Just with primary carb. Manual M20 4 speed. Doesn't happen in any gear but first with mild acceleration, not engaging outer carbs. When I nail it everything is fine. Factory setup with choke stove. Haven't checked the plugs.


Might be the accelerator pump in the center carb needs new plunger gasket....

You could test the squirt pattern and see if it looks good or sloppy.

You could also check timing, vacuum, and vacuum advance.


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## PontiacJim (Dec 29, 2012)

cij911 said:


> Might be the accelerator pump in the center carb needs new plunger gasket....
> 
> You could test the squirt pattern and see if it looks good or sloppy.
> 
> You could also check timing, vacuum, and vacuum advance.




Read Page 1, Post #8.


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## cij911 (Oct 25, 2017)

PontiacJim said:


> Read Page 1, Post #8.


Yes, I saw your post and am generally in agreement. He hasn't verified vacuum, total timing, or vacuum advance, nor have we ruled out center carb accelerator pump....


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## Rlamarche1 (Nov 22, 2016)

Thanks cij911. I think I'll forego the AFR gauge. As far as the center carb accelerator pump or gasket, wouldn't the sputter be there all the time, not just when hot? I realize there are several things that can cause this condition and I will have to eliminate them one at a time. Thanks for everyone's input.


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## geeteeohguy (Feb 2, 2008)

cij911, the reason it sputters in first gear when he takes off from a stop with a hot engine is probably because MOST people who drive these cars take off from a stop in 1st gear. By the time he gets the car rolling and pulls air through the radiator core, the issue is resolved. My Corvette clears up in about 6 car lengths. I'm a certified ASE Master Auto Technician who has been in the industry since 1979. Pontiac Jim has been around cars even longer than that. I have no intention of confusing the OP...just trying to lay it out and approach it as a technician. 

RLamarche: YES---if you had a bad accelerator pump, it would be even worse when cold, since cold engines need richer fueling. So the 'only when hot' accelerator pump issue is probably a false trail. My bet is that you are getting some boil-off due to underhood heat, as previously stated by Jim and I. As a PS, I have not used an AFR gauge (other than a smog machine) on any of my old vehicles in the past 40 years. Never needed to.


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## Sean Lyddy (Oct 4, 2018)

i was going to say something but you guys got it all covered all tho if they have a drop in Hall sensor to trigger the fire i would get rid of the points...i put one in a 64 Lincoln and it made a huge difference and it still looks like factory


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