The little screw is your pilot air screw. Factory setting is 1 1/4 turn out from bottomed out. The big screw is your slide height screw. If you have it turned all the way in just to idle your pilot jet is to rich. Find out what size pilot jet is in it. The carb slide screw should only be turned in enough to get the slide 1-2mm open at idle. Your main may be rich as well, but until you have the slow speed circuits right I wouldn't change it. The only other thing I can think of is possibly the needle jet is worn, it will totally mess up your you tuning on all throttle circits. Set the pilot screw first, then find out what pilot jet is in it and we can go from there.