Small Engines (Lawn Mowers, etc.): Lawnmower backfiring???? re:wont start, starter clutch, flywheel bolt

Question
RE: Won't Start... I couldn't post a reply for some reason... So I am doing it this way...

Sorry it took so long to reply back.  I discovered that this model does not have a seal or cap on the exhaust valve only the intake.  Thats solved.  Now I also discovered the problem was a sheered flywheel key.  I replaced it and it runs great.  I start cutting the grass for about five minutes and w/out hitting anything it suddenly backfires hard through muffler and shuts off.  When I check it out it has another sheered key. I've replaced the key three times. The last time I replaced it I tried to get the flywheel bolt a little tighter just in case and it backfired, shut off, and did not hurt the key.What is causing this.I have a few more ideas but could use some help.
Thanks,
Jason

Answer
Hi again Jason!
Number one - verify that there is a washer between the flywheel and the retaining device, whether it is a large nut or the starter clutch.

Number two- Make SURE this washer is bent into a cone shape.  This causes it to  act as a spring VERY IMPORTANT.  Without this washer and that shape the flywheel will move around adn the timing is SOOOO critical- it will backfire and cut off.

So- replace the key- one more time.  INstall the spring washer and torque the flywheel to at least 70 ft lbs (all you can muster on a 1/2" standard length socket wrench).

Lemme know ok?