First look for fuel delivery problems, supply line, tank, filter, VENT LINE, etc. Once your sure that ENOUGH fuel is getting to the engine, then it is time for tuning with patients. Set the needles to factory specs. Tune the LOW END FIRST! All your looking for is a smooth transition, don't try to fine tune it yet. Then get after the HIGH END with a good TACH. Peek the rpm then back off about 200 rpm buy making it richer. Fly the plane and make sure it continues to run through maneuvers. Then go back and tweak the low end again. A 1/6" turn will make a difference. I personally don't look for every rpm that I can get. As long as it runs good I leave it alone. If all else fails check the reed because they do wear out.