search "carb tuning" and you will find step by step instructions.  remember to first warm the bike up then when you are turning the screw out "counterclockwise" that you do it in 1/4 turn increments and give it half a minute between each turn.  basically you are listening to when the engine falters on either end (turning in, and turning out) those are your limits and then you turn out based on the average between the two limits.  the thread expains it perfectly