C3 very fast idle
Thread Starter
Heel & Toe
Joined: Feb 2026
Posts: 18
Likes: 1
C3 very fast idle
I finally got my 77 to start up, I replaced the fuel pump and electric choke, when I start it up it idles extremely fast, since the car has sat for 15 years, and hasn’t started in that time I’m worried to let it run at such a fast idle for so long, wondering what could be causing it (it idles at around 50-75% throttle.)
Melting Slicks
Joined: Feb 2018
Posts: 2,328
Likes: 724
From: Marietta GA
You will need to obtain information on the vacuum hose system. Temporary use a golf tee or plug the line going to the headlight vacuum system, there should be a plastic vacuum splitter behind the carburetor. If you intend to do your own service work, purchase a year specific Chevrolet Service Manual. Clueless Guessing, is not a way to work on the cars.
Melting Slicks
Joined: Apr 2021
Posts: 2,718
Likes: 2,163
From: Minnesota
Definitely probably sounds like a vacuum leak. What RPM is the engine actually turning at?
Like what was said, cap all vacuum ports on the carb and intake. If the high idle still persists I would wave an unlit propane torch at the base of the carb to see if your idle speed increases. If it does you have a bad mounting gasket.
Like what was said, cap all vacuum ports on the carb and intake. If the high idle still persists I would wave an unlit propane torch at the base of the carb to see if your idle speed increases. If it does you have a bad mounting gasket.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,137
Likes: 4,248
From: US-PNW
Pull forward on the throttle lever connecting to the cable. Actually, un-clip the cable from the carb and see if the rpms drop. If the cable or pedal is hung up in some way, it'll pull on the throttle lever and not allow it to return all the way.
If it's below 3000, I'd not worry about letting it run for extended time -- won't hurt the engine. If it does, then you're better off finding out now than when accelerating on the street.
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