I have a Kohler Comand 26 Hp with less than 100 hours that started out by dieseling at shut off and has now progressed to stumbling on accelleration and also back firing with a large flame out the exhaust when you reduce the throttle. Head gaskets were done last year to eliminate the oil consumption problem and the carb has been cleaned but I found no dirt or varnish. Kohler is sending me a new accellerator pump diaphragm but the old one was fine. The fly wheel key is also good. Carb is not adjustable on mixture but float level is good. This is a model cv25s on a Craftsman tractor that is 3 years old. I bought it used so I have no warranty and parts can get expensive if I start guessing. Any help or ideas would be great. I figure its getting extra fuel on decell to shoot the flame.