IFR's below 2500rpms or so pending the size of the main air bleeds. The main air bleed slows up or speeds up when the mains start to come in.
IFR changes will produce the largest a/f changes per swap. I swapped from .028's to .031's which changed my cruise a/f readings by 1.5 to 2.0 with no other change. Then once you get your off idle and cruise a/f in the range that you like, then use your air bleeds to tweak in your smaller a/f changes. I made a change in idle air bleeds by .003 (x 4 bleeds) and found an a/f change at cruise by .4 to .6.
Hope this helps.