Small Engines (Lawn Mowers, etc.): Techumseh detonation, woodruff key, compression stroke

Question
I am having problems with exploding fuel exiting into the muffler and causing it to glow red hot. The engine overheats and stalls out after a few minutes of operation.

I wrote on this subject previously to John senior but he is on vacation. He directed me to check the condition of the flywheel woodruff key and replace if necessary and change the spark plug. I have done both and the problem persists. I'm not sure where to go next. Valves?

Techumseh engine family is xtpx3 3582bf. The model number is 143.001103. Displacement is 358, if that matters.

The blower is a Craftman dual stage, model c950-52930-0, 11hp, 31 inch auger.


Answer
Hi Paul,
 If you have verified for sure that the flywheel key is not sheared, next i would check the valves to see if they have proper clearance although the sheared flywheel key is the most probable problem.  Did you remove the flywheel completely and inspect the key to make sure that it is not sheared or even partially sheared?  Also if the engine has been recently worked on i would verify the cam timing but to do this the engine would have to be removed from the equipment, the crankcase cover removed, and the engine turned to top dead center on the compression stroke to see if the indexing marks on the cam gear and crankshaft line up.