I was using our lawn tractor the other day. It was running fine. Has a 20 HP Kohler. All of a sudden it started blowing smoke like crazy and soon stalled and quit running. Let sit for a bit, checked oil, and started again. Got started but would not keep running. Still smoking bad. Where should I start? Could this just be a ring that's bad? Or is it possible there is a easy fix? Probably 200 hours on machine.