[vector1]

The test for IFR's / idle air bleed combo is adjust idle for best mixture, then turn up the idle speed to about 1200 - 1400, under where the main circuit begins feeding fuel. Turn the idle screw out to see if the idle speed increases with the additional enrichment. If the engine rpm increases, you probably need more IFR. You can also turn the idle speed screw in to see if it is too rich. If turning the mixture screw in increases engine rpm then the IFR is too rich. When the IFR is correct, the engine rpm should decrease an equal amount whether you are turning the mixture screw in or out.

quoted from troy patterson