The shim is inside the carb throat the o ring is before the shim where the clamp bolt is there are 2 areas one before the clamp on the top other is that split. After that. Make sure that the slider bottoms far enough. The. Holes in the tube of the carb are clogged the jet fell out or is clogged the cdi ground wire or spark cap is bad the killswitch is grounding itermitantly wrong plug heat try a 6 hs.