I have a Yard Machine mtd 16.5 hp tractor mower 13a0695G062 64448. It stopped running 2 weeks ago. I put on a new magneto/coil. Ran fine. Today it struggled to start. I disconnected ground from magneto/coil, it started ran for 5 minutes backfired then died. It won't start again. Please help me

Did you forget to put the woodruf key back in the flywheel, it sounds exactly like that's what happened? The flywheel WILL slip on the crank if its sheared or missing.