Hi, i have a exmark lazer with a kholer 2 cylinder engine, its been backfiring and loosing power. its not really backfiring as much as sputtering i guess or it does kinda make a pop sound as its running. any ideas what it could be? i repalced plugs, air filter and sprayed this Amsoil spray into the intake to clean the carb/engine. it kinda fied the problem for a week but now its back.