IIRC in general, turning the "mixture" screw out will make it richer. There is an idle air jet (carb throat) and idle fuel jet (float bowl). These two screwed in jets combine to control the mixture and the screw controls the volume of that mixture that enters the carb throat on the motor side of the butterfly. This mix combines with mostly air that gets by the butterfly. Then the idle speed screw opens the butterfly a little and/or lifts the slide (either with vacume on the CV carbs are mechanically). This adds a little extra air so you can open the idle volume screw for ballance. Adjusting the idle speed and mixture screws together should give the best results. On some bikes (FZ1) there are multiple holes in the bottom of the carb throat, three behind and one in front of the butterfly. The extra holes are there to help with the lean transition (bog) from the idle circuit to the midrange circuit. Kinda like what the accellerator pump does on the pumper carbs.