I have been having problems with back firing and some black smoke. I have about 560 hrs on this lawn tractor. I am not sure where to start. I have changed the oil and the spark plug. It seems if I let the engine cool off a bit before I turn it off that stops the back firing. Also the manual encourages you to run the 425 at a higher speed (engine), I am not sure if this is correct or not....just my 2 cents. At any rate, any ideas out there?


Thanks!