My tractor starting backfiring. When the throttle is where it is supposed to be when mowing the lawn, it begins to backfire.

This could be a timing issue or a carb problem. Do you recall anything that happened about the time this started like hitting a rock or stump or changing a fuel filter or tank?

I changed the fuel filter this spring. The tractor ran well until just few weeks ago. I took the fuel filter out and noticed that there was some kind of deposit so I cleaned it out. However its still backfiring.

What engine do you have on this unit.

I got my tractor repaired. It had a cracked carborator and a broken key.