Pilot screw-controls the amount of fuel/air mixture in the idle(pilot) circuit
Air screw-controls the amount of air entering the mixture in the idle(pilot) circuit
Fuel screw-controls the amount of fuel entering the mixture in the idle(pilot) circuit
Don't know which/if any carbs use air or fuel screws but I know the Mikuni's have an Air JET, Pilot(fuel) JET and Pilot(idle mixture) screw that adjusts the amount of air/fuel mixture exiting the carb during idle. Turn the screw out, more mixture is allowed in (richens), turn it in, less mixture is allowed in (leans).