If that carb hasn't been molested the stock jetting is 78 all the way around,with 73 jets someone probably has richened the idle mixture to cover up a lean stumble.put the stock jetting back in and reset the idle mixture and adjust from there. a large carb on a small engine needs more jet and smaller high speed air bleeds, you don't have the velocity to tip in the boosters soon enough to prevent a stumble without overly rich idle settings.Bill