There's a fast idle screw hidden on the underside of the throttle linkage - if it's wound all the way in there is part of your idle issue. Wind it out a few turns and monitor the idle rpm. You'll need to reset the idle stop adjust screw and the air/fuel mix as well. When all the base settings have been tampered with it takes time to dial it all back in. If the choke butterfly is snapping shut the tensioner spring will need to be adjusted as well. The butterfly should only have a very light load on it.