Small Engines (Lawn Mowers, etc.): Backfire thru carb, backfiring

Question
riding mower has been backfiring through the carb for the last couple of mows, then i mowed about 1/2 hour today and went back to mow, mower is backfiring through carb so bad it wont hardly run

Answer
The first thought would be to check the flywheel key.  If it's sheared, then the flywheel has moved and the ignition timing will be off.

Next would be a valve problem and a carb that's running very lean.  As for the valves, a loose or bad valve seat or a sticking valve might be the case.  But I'd start simple and check the flywheel key.  Let me know if you have any questions.  Thanks, PK.