we mowed two yards today. while i was at school, my dad checked my rider's engine and adjusted the main jet on the carb and we had no trouble with it today. it runs great at an idle now! no backfiring yet. one bad thing about it, that engine uses oil like crazy! its because the cylinder is worn out and oil gets in it. if i rub my fingers on the muffler, they will turn solid black from the carbon on the muffler. i know we need to clean the exhaust port very soon.