adamdinat

How is the fast idle on a Holly Carb supposed to work? It seems the engine is always idling fast 1200RPM . Once warm I can kick it down to 1000 or 850 rpm depending on how hard I hit the pedal. At the next light it is back up to 1200? What triggers the Fast idle cam to change to the lower position and stay there?

Wrencher

I'll throw a couple of thoughts out there on this. Most common problem on these is a worn throttle shaft on the primary side, especially if it uses the stock return spring. With the throttle cable pulling above and the sring pulling back below, it uses the alloy base as a fulcrum or pivot point. Bad design. The return spring should have been setup to pull forward and hook up high next to the cable. That takes all the load off the throttle shaft. Basically, the throttle plates do not return to the same place every time, unless you "snap" the throttle. Common on Q-jets as well.

Next problem is a throttle cable that is fully extended at idle. There has to be a bit of slack where it hooks to the carb, or it will hang the throttle.

Fast idle cams typically either hang up and stay there, or work. The exception would be if the choke is not releasing (not getting enough heat) and thus the fast idle isn't dropping all the way down. An easy way to check it (engine warmed up) is to push down on the cam weight (RH side of the carb, air cleaner off, it is a crooked, plastic arm with what looks like a large BB molded into it) and see if it drops ("clicks") down and the idle also goes to normal.

Hans