I have a 2007 60" Super Z with xr7 deck and 27 Horse Kholer engine. Ever since I bought this mower the motor has always had backfiring problems. A colleague of mine who bought the same mower at about the same time says he also has this problem. If you dont let the engine idle for 5 minutes the motor backfires when you shut it off and sometimes still backfires when you wait. Does anybody else have this problem? Is it just a property of this particular engine model. Any suggestions Hustler?