64 GTO 389 Tripower acceleration - Pontiac GTO Forum
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post #1 of 20 (permalink) Old 10-19-2018, 09:11 AM Thread Starter
 
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64 GTO 389 Tripower acceleration

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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post #2 of 20 (permalink) Old 10-19-2018, 05:56 PM
 
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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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post #3 of 20 (permalink) Old 10-19-2018, 07:26 PM Thread Starter
 
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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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post #4 of 20 (permalink) Old 10-19-2018, 09:27 PM
 
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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-t...m_content=hero
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post #5 of 20 (permalink) Old 10-20-2018, 07:07 AM Thread Starter
 
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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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post #6 of 20 (permalink) Old 10-20-2018, 08:14 AM
 
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Originally Posted by Rlamarche1 View Post
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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post #7 of 20 (permalink) Old 10-20-2018, 09:07 AM Thread Starter
 
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Yes I am running a points distributor. The coil/points issue is certainly something to be considered. Thanks!
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post #8 of 20 (permalink) Old 10-20-2018, 09:27 AM
 
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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.
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post #9 of 20 (permalink) Old 10-20-2018, 10:17 AM Thread Starter
 
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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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post #10 of 20 (permalink) Old 10-20-2018, 03:02 PM
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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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