adjust your idle with the air screw not the thumb screw.  Do like everyone said and set the slide height (thumb screw) to about 2mm.  Adjust your throttle cable so there is no play in the cable.

If your pilot size is close you'll be able to turn the air screw one way or another and the idle will change. Out=more air .  In =less air.  if you have to go beyond 2 turns out, you will need to drop your pilot 1 size and try again.  If you have to under 1 turn you will need to increase your pilot one size.  adjust till you get it to idle.  If you get no change in idle no matter how many turns in or out on the air screw, your pilot is way off.

good luck