I am assuming this is a 393 series make sure rpm sensor is adjusted properly it is located in bell housing and works off of ring gear if you removed it then readjust. to readjust loosen up push down until it touches ring gear the pull up 1/8 -1/4 in and tighten Linde calls it a speed acquisition switch
If that checks out check the mixer (carb ) they have a tendency for the internal disc to stick