[30AAFord]

I think you are referring to the mixture screws - on the 59A carb, there are two (one for each barrel/bank of cylinders). There is only one idle adjustment screw and that is part of the throttle butterfly. When you screw it in, you are increasing how much the throttle stays open while you are idling. In order to keep my truck running, that screw has to be fully threaded in (until it stops), substantially increasing the idle speed of the engine. Anything less and the engine stalls out. I know this isn't right.