Hi, I just converted my '79 F100 to a 4 barrel setup with a new edelbrock intake (3721) and holley carb (0-80457SA). She started right up after everything was in place but when I rap the throttle after it warms up to bring it to normal idle it changes but is still to high, I don't have a tach so I'm not sure but guessing around 1000 rpm still. Turning the curb idle screw made no difference but I did notice that if I push back pretty hard on the throttle at the carb it would lower to where it should be. The throttle cable itself is not holding it open, there is still slack in the cable when not pressing the pedal. What could be holding it slightly open?

 

The 1st thing I would check is the carb base plate...loosen and retighten slowly & consistently all attachment bolts/nuts simultaneously....failure to do this can cause the base plate to warp.....

 

Turns out it was the fast idle can getting hung up, I just manually pushed it down and the idle went right down to where it should be. Haven't had any problems with it since.