First, a couple of things to remember. The idle air/fuel screw is not really supposed to be used to control the idle speed. For the Autolite 1100s there is a screw under the choke adjustment that controls the idle speed. It does this by cracking open the throttle plate. Other carbs have these as well, I'm just not sure of the location.
Start here:
1) Turn the idle mix screw all the way in (until the spring is compressed) and then turn it out 2 complete turns. This will give a good starting point.
2) Start the car. Hook up a tach, and run the RPMs down to the desired level using the idle speed screw on the back of the carb (once again, 1100 carbs).
3) Now adjust the idle air/fuel mix screw. Do this one of 3 ways: By Ear, By Tach, or by Vac gauge.
3a) Slowly turn the aif/fuel mix screw in until you see or hear a drop in RPMs or the car starts running rougher. Now turn the screw out until you hear the car go up in RPMs. Adjust the screw until you have the max RPMS/Vac at that throttle plate setting. The RPMS will go up and down as teh carb goes from lean to rich. Where the RPMS/Vac are the same, that is where the carb is set right.
As you do this, double check your timing. You may have to repeat the process a couple of times to get it just right.
Slade
