C3 not running smoothly after winter break
Thread Starter
Intermediate
Joined: Aug 2024
Posts: 32
Likes: 4
C3 not running smoothly after winter break
Hi everyone, it's been a while since I last wrote, and I hope you're all doing well!
I'm reaching out regarding my 1974 C3. The car was sitting idle for about three months due to the registration process in Italy (which was successfully completed). Yesterday, I took it out for a drive after a long time (although I had started it a few times and let it run while stationary in the garage), and it didn't feel great.
The engine doesn’t seem to be running smoothly, especially at low RPMs (up to 2000 RPM). Additionally, at one point, it felt like the power delivery cut out for a fraction of a second.
On top of that, I heard a few backfires (which improved after running for a few minutes).
What could be the issue? A friend suggested it might be the distributor, the ignition coil, or possibly a dirty carburetor.
Thanks in advance for your opinions!
P.S. The car will be at a mechanic’s in the next few days for a full service.
I'm reaching out regarding my 1974 C3. The car was sitting idle for about three months due to the registration process in Italy (which was successfully completed). Yesterday, I took it out for a drive after a long time (although I had started it a few times and let it run while stationary in the garage), and it didn't feel great.
The engine doesn’t seem to be running smoothly, especially at low RPMs (up to 2000 RPM). Additionally, at one point, it felt like the power delivery cut out for a fraction of a second.
On top of that, I heard a few backfires (which improved after running for a few minutes).
What could be the issue? A friend suggested it might be the distributor, the ignition coil, or possibly a dirty carburetor.
Thanks in advance for your opinions!
P.S. The car will be at a mechanic’s in the next few days for a full service.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Gummed up carburetor certainly fits all your symptoms. Obviously your mechanic will check all the basics as well. But a good cleaning of the carburetor is likely the solution to your issue.
Melting Slicks
Joined: Jul 2010
Posts: 2,762
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From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
I would start with fresh gas first since this is the cheapest/easiest.. Start with a can of Seafoam to help clean it out till you get fresh gas!
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Thread Starter
Intermediate
Joined: Aug 2024
Posts: 32
Likes: 4
regarding fuel freshness: i left one liter, maybe two, during winter break. Then yesterday I did 10 liters. Is it wrong? Do you usually remove all the fuel for winter break? thanks for your support!
Thread Starter
Intermediate
Joined: Aug 2024
Posts: 32
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is there a video of how I can apply seafoam?
thanks for your support
Last edited by Vette1974IT; Mar 10, 2025 at 04:14 AM.
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Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I really doubt Seafoam is available in Italy. Unless Italy has its own source of Amazon, perhaps.
You may have your own version of Seafoam in Europe.
Basically, it's just a fuel tank, lines, and carb cleanser. You pour some in the tank and some down the carb at a fast idle.
For what it's worth, my first run down the road in the spring is on 6 cylinders. Then 7. Then 8.
Clears up after a couple miles. Then I fill with fresh gas.
I wouldn't be too concerned with your misfire issue at first. Condensation under the distributor cap.
Rusty plugs, carb full of moisture, sticky valves, lifters not pumping up, etc.
After several miles and the issue continues, then you have a problem.
You may have your own version of Seafoam in Europe.
Basically, it's just a fuel tank, lines, and carb cleanser. You pour some in the tank and some down the carb at a fast idle.
For what it's worth, my first run down the road in the spring is on 6 cylinders. Then 7. Then 8.
Clears up after a couple miles. Then I fill with fresh gas.
I wouldn't be too concerned with your misfire issue at first. Condensation under the distributor cap.
Rusty plugs, carb full of moisture, sticky valves, lifters not pumping up, etc.
After several miles and the issue continues, then you have a problem.
Last edited by HeadsU.P.; Mar 10, 2025 at 09:11 AM.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,140
Likes: 4,248
From: US-PNW
I'd do as HeadsU.P. said and run new gas through it for a bit. Take it up to 4000 a few times and see how it behaves after a few heat cycles.
Thread Starter
Intermediate
Joined: Aug 2024
Posts: 32
Likes: 4
I really doubt Seafoam is available in Italy. Unless Italy has its own source of Amazon, perhaps.
You may have your own version of Seafoam in Europe.
Basically, it's just a fuel tank, lines, and carb cleanser. You pour some in the tank and some down the carb at a fast idle.
For what it's worth, my first run down the road in the spring is on 6 cylinders. Then 7. Then 8.
Clears up after a couple miles. Then I fill with fresh gas.
I wouldn't be too concerned with your misfire issue at first. Condensation under the distributor cap.
Rusty plugs, carb full of moisture, sticky valves, lifters not pumping up, etc.
After several miles and the issue continues, then you have a problem.
You may have your own version of Seafoam in Europe.
Basically, it's just a fuel tank, lines, and carb cleanser. You pour some in the tank and some down the carb at a fast idle.
For what it's worth, my first run down the road in the spring is on 6 cylinders. Then 7. Then 8.
Clears up after a couple miles. Then I fill with fresh gas.
I wouldn't be too concerned with your misfire issue at first. Condensation under the distributor cap.
Rusty plugs, carb full of moisture, sticky valves, lifters not pumping up, etc.
After several miles and the issue continues, then you have a problem.
so, if i understood correctly, some in the tank with low gas, plus some in the carb with fast idle (i assume i have to remove the air filter to do it, right?)
then I run the vehicle for a while and then more gas in the tank, correct?
best
aa
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Correct. It takes a fast idle once you start introducing Seafoam (extra fuel) down the throat of the carb.
Go slow & steady, it will try to stall-out.
Your neighbors will love the smoke screen. But eventually it goes away.
Go slow & steady, it will try to stall-out.
Your neighbors will love the smoke screen. But eventually it goes away.
Thread Starter
Intermediate
Joined: Aug 2024
Posts: 32
Likes: 4
I have already had discussions with my neighbrs
Any risk the car will turn off?
Race Director
Joined: Mar 2017
Posts: 11,953
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From: Virginia
What is your timing set to?
What you described is how my car ran when I accidentally put the vac advance on the wrong port. On ported vacuum, it ran like crap, but was "original". With manifold vacuum, the extra 10-12 degrees of advance made all the difference for a smooth idle.
Perhaps it's that simple?
What you described is how my car ran when I accidentally put the vac advance on the wrong port. On ported vacuum, it ran like crap, but was "original". With manifold vacuum, the extra 10-12 degrees of advance made all the difference for a smooth idle.
Perhaps it's that simple?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
No big deal. Restart. Hardly a risk.
Jazz the snot out of the throttle. And don't put your face over the carb if you like your eyebrows.
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
I would find a bottle of BG 44K and put in the gasoline and just "drive it" clean. Nothing works like BG 44K does, hundreds of new car and used car dealers use it every day for cars under warranty that need to run better or idle smoother. It is available on Amazon and in other parts of the world. BG 44K makes my cars all idle as smooth as glass, this stuff is amazing
They make kits for serious cleaning of the intake parts that use a couple different bottles of liquid. One goes in the fuel tank and the other is drawn into the injection system through a vacuum line. One of my neighbors used Seafoam and another neighbor called the fire department not knowing that all that smoke is "normal". That smoke was nasty and thick.
They make kits for serious cleaning of the intake parts that use a couple different bottles of liquid. One goes in the fuel tank and the other is drawn into the injection system through a vacuum line. One of my neighbors used Seafoam and another neighbor called the fire department not knowing that all that smoke is "normal". That smoke was nasty and thick.
Racer
Joined: Dec 2022
Posts: 303
Likes: 87
I would find a bottle of BG 44K and put in the gasoline and just "drive it" clean. Nothing works like BG 44K does, hundreds of new car and used car dealers use it every day for cars under warranty that need to run better or idle smoother. It is available on Amazon and in other parts of the world. BG 44K makes my cars all idle as smooth as glass, this stuff is amazing
They make kits for serious cleaning of the intake parts that use a couple different bottles of liquid. One goes in the fuel tank and the other is drawn into the injection system through a vacuum line. One of my neighbors used Seafoam and another neighbor called the fire department not knowing that all that smoke is "normal". That smoke was nasty and thick.
They make kits for serious cleaning of the intake parts that use a couple different bottles of liquid. One goes in the fuel tank and the other is drawn into the injection system through a vacuum line. One of my neighbors used Seafoam and another neighbor called the fire department not knowing that all that smoke is "normal". That smoke was nasty and thick.