1920 Fast Idle Cam

[dcdman67]

Hi all. I just rebuilt my 1920 and I am having some issues with the fast idle cam. I have reassembled and reinstalled the carb. Whenever I hit the gas on the car, the cam does not return back to the second step, and instead sits on the first step at a very high idle. The cam has a ton of play in it. Do I need to bend the rod so that there is no play?

Also, I am having a hard time starting the car without starter fluid. Something seems to be amiss.

Any help is appreciated!

 

[slantsixdan]

It sounds as if there are some problems with your choke linkages. You'll want to go through and make sure the whole enchilada is working correctly: the choke thermostat (not rusted all to hell, not dead of old age, pushrod not bent out of its original shallow-Z configuration), the choke pull-off (operational, not leaky), and the links between the pull-off and the choke lever and the choke lever and the fast-idle cam. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

 

[dcdman67]

Hi Dan. I took the carb in for a rebuild and all is well. The bushings and linkages needed to be repaired.

 

[BillGrissom]

... I hit the gas on the car, the cam does not return back to the second step, and instead sits on the first step at a very high idle. The cam has a ton of play in it. ...

Seems you are talking about the section from the Holley 1920 manual shown. The manual specifies "what to do", but doesn't fully explain "how it should work". My understanding is that the fast-idle position the cam offers to the fast-idle screw is a function of the thermostat rod, not whether you have blipped the throttle or not. But, there is interaction of the cam with the "choke unloader" (vacuum diaphragm), so you may be correct. The manual only talks about adjustments with fast idle on the 2nd stop and never says when it should fall on the 1st stop. Perhaps that should be when cranking (no vacuum on unloader). Strangest sentence is "fast idle speed is adjusted after ... engine warmed up". Isn't fast-idle "off" once the engine warms up (choke fully open, cam where fast-idle screw doesn't touch).

If you don't have the manual, download (web search), follow the adjustment instructions, and insure your choke unloader works. A hand vacuum pump is best (manual doubts you can suck 15" Hg). A poor-man's method is to push in the stem, block port w/ finger, and see if stem stays retracted. We might guess that you have a 1967 engine (always tell). If so, your choke is adjustable ("R" = rich, "L" = lean), so might need adjusting so it doesn't push so hard when cold (rotate thermal spring holder towards "L"). The manual I have just states, "early divorced chokes were adjustable, even though the adjustment specifications were not given".