Question: Fast Idle Adjustment

[antique78vette]

Can any C3 experts out there please tell me or show me where the fast idle adjustment screw is on my stock 78SA L48 carb?


thanx again for your help!!!!!!!!!!!!!!!

mike

 

[TimAT]

I'm no expert, I own 3 of them. If I had any sense I'd find something else to do with my time.

The stock carb is a Quadrajet- the fast idle is on the right side kind of hidden by the choke linkage. At the front of the carb there is a small vacuum diaphragm- that's the choke pull-off. I suspect your has what's called a "divorced choke". All that means is the choke thermostat is mounted to the manifold with a rod connecting it to the carb. Even if it's an electric choke there will be a thermostat with a wire running to it.
When it's cold, and you pump the gas the 'stat will cause the choke to close and the fast idle cam to step up. If you watch the right side of the carb when it cold, give it some gas- (not running) you can see the fast idle cam move up and see the adjustment screw. remember- as soon as it starts the engine needs more air so the choke pull-off opens the butterfly via vacuum. 17* comes to mind, but it's been a long time. Sorry I dont' have a picture- but someone will either have a good picture or a better description.

 

[73shark]

On my '73, you have to bend the tang that contacts the fast idle cam that's connected to the choke to adjust the fast idle. Remember that you adjust fast idle w/ a fully warmed up engine.