Small Engines (Lawn Mowers, etc.): backfire lawn tractor and engine wont turn over, cub cadet 1042, key way

Question
I recently had to replace my key way pin on Cub Cadet 1042 about a month ago when the engine wouldn't turn over.  The lawn tractor ran good until I started and drove it out of the barn and it sat for 3 hours and when I went to start the engine the engine again wouldn't turn over.  The next day when I tried to start it it backfired and the engine will still not turn over.  It has backfired in the past after the engine was turned off.  Even if I idled down the engine.  What's wrong.  Do I need to replace the key way pin again? I think I have a lemon.

Answer
Replace the spark plug, shut the mower off at full speed and see what happens.   If this doesn't help reply back and tell me what your old sparkplug looks like, Powdery block, light tan, oily black,etc...

The only reason you should ever have to replace the flywheel "key" is because the nut on the flywheel wasn't tightened tight enough.
 This freakin nut has to be TIGHT!!!!