Can anyone explain in basic terms what the "Fast Idle Cam" is for and when it is used? For that matter, what is "Fast Idle"?

I've got a motorcraft 2150 carb from the early 70's that the set screw (for limiting choke pull down) is frozen and won't budge. Should I be concerned? It currently allows the choke to be pulled down too much...

Thanks in advance.

 

Cars have a "fast idle" mechanism: this idles the engine faster when cold. A carburated car has a fast idle cam with several steps. If started and left to idle, it will stay on the fastest step of the fast idle cam even after it starts to warm up. You have to tap the gas pedal and "kick the idle down". This fast idling of a semi warm engine is not good for it.

 

Ah ha! Thanks, Soaring. Now I know what's happening when it idles lower after a quick tap!

 

The automatic choke controls how much it set the fast idel up. When its colder and needs more choke, then it will idle faster.