C3 Problems with running
Thread Starter
Cruising
Joined: Sep 2012
Posts: 14
Likes: 0
From: Pittsburg KS
C3 Problems with running
So I have been having this problem for a while but it only happens like once a month. When I start the car it starts up fine but the RPMs fluctuate about 500rmp without me ever touching the pedal. When I put it in gear it wants to die but if it doeswhen I try to accelerate it runs as if I were out of gas but i am not. It isn't water in the tank(put heat in it to remove and I have used many different gas stations and they all do the same thing) my choke pull off was not working correctly previously but I opened it all the way so it would not close which should eliminate that. Then the next day I start it it runs fine until the next month or few weeks. when it is messing up if I press on the gas and hold it in the same position it will speed up and slow down and speed up and slow back down all without me changing my foot pedal position. Anybody have any suggestions? thanks even though all the problems i still love my vettetill love my vette. 
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
Does this problem go away once the engine warms up? Have you tried adjusting the idle mixture screws? Have you checked the 4 bolts holding the carburetor to the intake to see if any of them are loose? Have you sprayed carburetor cleaner around the base of the carburetor to check for a vacuum leak?
Melting Slicks
Joined: Aug 2012
Posts: 3,487
Likes: 83
From: Titusville Florida
Sounds like carb issue to me, needs a rebuild or new. But then someone smarter than me may come along and have a different idea.
Last edited by AirborneSilva; Dec 4, 2012 at 12:27 PM. Reason: new info
Heel & Toe
Joined: Dec 2012
Posts: 19
Likes: 0
I agree with MelWff, I would check the 4 bolts holding down the carburator to the intake. My vette would have problems where it would run fine and then warm up and then die. I replaced the distributor, cap & rotor and it still would randomly die on me after running for some time. One of the times I noticed the choke was sticking so I could either rebuild the original carb or buy a new one. I went with buying a new one. To my surprise, when I went to remove the old carb, the bolts holding it down could literally be turned by hand. I never would have thought to check for a vacuum leak at the carburator as the car started, worked fine but would randomly die on me while I was driving. I swapped out the carb with a new one, replaced the gasket and the car stays running now but I can see where a vacuum leak could make your RPM's act they way they are.
Instructor
Joined: Jul 2010
Posts: 120
Likes: 0
Sure sounds like a vacuum leak to me. Id check all the hoses and do what Mell says . . spray carb cleaner all around any vacuum connections but try not to get any in the throat of the carb . . if the idles shoots up theres your problem.
Melting Slicks
Joined: Aug 2012
Posts: 3,487
Likes: 83
From: Titusville Florida
I agree with MelWff, I would check the 4 bolts holding down the carburator to the intake. My vette would have problems where it would run fine and then warm up and then die. I replaced the distributor, cap & rotor and it still would randomly die on me after running for some time. One of the times I noticed the choke was sticking so I could either rebuild the original carb or buy a new one. I went with buying a new one. To my surprise, when I went to remove the old carb, the bolts holding it down could literally be turned by hand. I never would have thought to check for a vacuum leak at the carburator as the car started, worked fine but would randomly die on me while I was driving. I swapped out the carb with a new one, replaced the gasket and the car stays running now but I can see where a vacuum leak could make your RPM's act they way they are.
See,
I told you people smarter than me would come along
Instructor
Joined: Jul 2010
Posts: 120
Likes: 0
Carbs just dont go bad not sure why people go buy new ones unless its because they specifically want something different. For example I went from a 750 with vac secondaries to a 650 with mechanical secondaries so yea a new one was needed. If your carb is the correct one and its having issues then a rebuild is all you need. Now yes you can have some issues like possibly a worn throttle plate shaft or something causing problems but thats pretty rare.
Heel & Toe
Joined: Dec 2012
Posts: 19
Likes: 0
In my case, having the car die on me while driving and sometimes not being able to drive to a shoulder left me leary of the car as a whole. All it really needs is a good cleaning but because the car died on me about 7 times before and I swapped out allot of parts already, I felt better with going with a new carb. My confidence in the car staying running now is much better than if I would have rebuilt the old one. In my case it was more of a psychological need to change the carb then the old one no longer working. I feel more confident that the car won't leave me stranded anymore. It got to the point where I could tell when I had seconds to pull over before the car died-not a good feeling.
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Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
You might want to look inside the distributor and make sure the advance weights and vacuum can are working.
Thread Starter
Cruising
Joined: Sep 2012
Posts: 14
Likes: 0
From: Pittsburg KS
This happens when the car is cold and warm. After viewing the comments, I started checking to make sure that all the bolts were tight on the carb and found that one of the bolts was stripped out and just sitting in the hole. I have aluminum heads so I am planning on tapping it out but I have to find another stud first. I am thinking of switching carbs. Right now I have a Holly 4 barrel double pumper on it and it seems a bit excessive for an every day driver. I am thinking Edelbrock, but I have no clue as to which one, thunder or performance series or anything. I don't really care about blowing people away I just want one that doesn't need adjusted every day like mine now.
Melting Slicks
Joined: Aug 2012
Posts: 3,487
Likes: 83
From: Titusville Florida
This happens when the car is cold and warm. After viewing the comments, I started checking to make sure that all the bolts were tight on the carb and found that one of the bolts was stripped out and just sitting in the hole. I have aluminum heads so I am planning on tapping it out but I have to find another stud first. I am thinking of switching carbs. Right now I have a Holly 4 barrel double pumper on it and it seems a bit excessive for an every day driver. I am thinking Edelbrock, but I have no clue as to which one, thunder or performance series or anything. I don't really care about blowing people away I just want one that doesn't need adjusted every day like mine now.
http://www.autozone.com/autozone/acc...er=516472_0_0_
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
IF your local Orscheln store has bolts they should have an assortment of studs too. Just a bit north of you we have a couple of them that put 99% of the hardware stores to shame. Bolts and screws from 4-40 to 1-1/2 in more lengths than you can count, and most of them in all sizes from Grade 3 up to Grade 8. Plus all the nuts and washers.
