Hi all, I have a '73 400 with the stock Motorcraft 2100 carb. The carb uses a throttle positioning solenoid to hold the idle while the motor is running, then the throttle plates rest on the standard idle screw when the motor is shut off. If this screw is set so that the plates are too far open, the motor will diesel when shut off.

Here's what I need help figuring out. When I shut the motor off, it diesels because the throttle plates aren't being allowed to close. Not because the idle screw is set too far open, but because the throttle shaft is catching on the very end of the fast idle cam. It seems like there are three steps to the cam...the highest, which the engine starts on, then the second step (with the V mark) where the engine idles while the choke opens...then there is that third lowest one. That's where it's catching.

I have the hex screw on the fast idle arm set so that when the choke plate is in the pull-down position, the fast idle cam falls so that the throttle arm lands on the V mark. No matter how much I mess with that screw though, I can't get the fast idle cam out of the way so that the throttle shaft can rest on the standard idle screw and close enough so that the motor won't diesel.

It used to be so that the throttle plates would close substantially when I shut the motor off, but now, there isn't much difference between the plate opening when the motor is running and when it shut off. I have no idea what changed this.

Anyone know what to do?

 

Can you put a slight bend in the rod to the fast idle cam so that it is pulled a little farther out of the way?