C3: Carb trouble
Thread Starter
2nd Gear
Joined: Dec 2024
Posts: 2
Likes: 0
From: Bay area
C3: Carb trouble
I’m having a bit of trouble, I have 74’ C3 with a pretty new Edlebrock 1406. The problem I am having is when I shut off the car it kinda diesels and when it finally turns off it just sprays fuel from the carb. I think this might be a timing issue but have no idea, any thoughts? I have a video for reference (sorry for the low quality)
Tech Contributor
Joined: Aug 1999
Posts: 14,385
Likes: 6,413
From: At my Bar drinking and wrenching in Lafayette Colorado
Run-on after shutdown is caused by excessive idle speed (excessive throttle opening) at shutdown. Either lower your idle speed, or fix your timing so you can decrease the throttle opening at idle.
Melting Slicks
Joined: May 2021
Posts: 2,291
Likes: 1,332
From: Fleming Island, FL
Lowing the idle will help stop the run on. But the real cause is another ignition source in the combustion chamber other than the spark plugs like hot spots from carbon build up. Get a can of "Mopar combustion chamber cleaner". It's a little hard to find but that stuff really works. I've heard that using too hot of a spark plug can cause run on but I've never seen it personally.
Le Mans Master
Joined: Oct 2010
Posts: 6,952
Likes: 858
From: melbourne florida
2023 C3 of the Year Finalist - Modified
I remember back in the day when politicians fancied themselves automotive engineers . The forced emissions equipment on cars and they practically all ran like that.
Race Director
Joined: Mar 2017
Posts: 11,978
Likes: 4,528
From: Virginia
What is your timing set to? If you can't lower your idle, check for vacuum leaks. I'll hold off on bashing that carb until after the obvious fixes. 
Did anyone else watch the video? That's not run-on. Or if it is (and your car runs?), perhaps one or more intake valves are stuck open? Have you done a compression and/or leakdown test?
Did anyone else watch the video? That's not run-on. Or if it is (and your car runs?), perhaps one or more intake valves are stuck open? Have you done a compression and/or leakdown test?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette & Porsche 911: How Two Icons Conquered the Last 25 Years
Joe Kucinski
2027 Chevrolet Silverado 1500 First Look: Everything You NEED to Know!
Michael S. Palmer
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
