Turn the idle mixture screw in just until it’s seated (over tightening will damage the screw), and then back it out 1.5 turns. This is the initial setting, final adjustments will be made on a running engine.
NOTE: To lean the idle fuel mixture on the 28 series, you turn the idle mixture screw OUT (counter-clockwise), to lean the mixture on the 228 series you turn the idle mixture screw IN (clockwise). The idle mixture screw functions backwards from traditional carb setups on the 28 due to the design and idle mixture screw placement.