Try this. Step 1. Take the carb off the engine. Take a long screwdriver and from the engine side pop the welch plug in the rear of the carb out of the back of the carb.
Now loosen the screw on the butterfly slightly,, it needs to stay a little snug.
Open the throttle WOT.
From the welch plug or back side push the butterfly to the engine side,, there's always a little slack there. Tighten the screw.
Now when the butterfly is in the closed or idle position most of the idle air will pass directly by the idle fuel hole.
This will usually clean up the idle quality and make the engine easier to start.
If this doesn't completely cure the problem let us know and we'll go to step 2.