Got the top end rebuild complete on the Big Red so now it is time to break it in. After I got it running I found out that after I set the idle speed I would rev the engine and the idle speed would not return to the set speed – it was much higher. I was thinking about an air leak or throttle cable sticking. I sprayed some carb cleaner around the carb and intake manifold with no change. I inspected the throttle cable and it was good. I noticed that when I was adjusting the idle it seemed inconsistent when I turned the idle adjustment screw. This gave me the clue to what was going on. I took the slide off of the carb and noticed that someone had screwed in the idle adjustment screw to the point where it put a divot in it. This caused the problem since the slide would get caught in the divot after the throttle was opened. The divot put the slide at a higher position on the return so it would raise the idle speed. The solution for this issue was to take a needle file and file down the idle taper in the slide. The atc idles great now.
Divot on the idle taper on the slide filed down