Small Engines (Lawn Mowers, etc.): Tecumesh, toro wheel horse, cam shaft

Question
Hi, first off i have a toro wheel horse 8-25 with a tecummesh 8 hp engine. Its an old tractor and it starts fine but it surges and backfires excessivly. i have changed the plug and attempted to ajust the carb but nothing seems to solve the surge/ backfiring problem...

Answer
It sounds like your engine is out of time.  The first thing to check would be the flight will key.  Remove the lower housing that covers the flywheel removed the flywheel nut and remove the flywheel.  If broken replaced with new flywheel key.

Next would be checking the valves and valve timing.  To do this remove the engine breather and measure the valve clearance.  If valve clearance is okay the engine will need to be disassembled to check the timing.  Timing is a small mark on the cam shaft gear and the crankshaft gear.  They must align.

Although I think it is in the timing you could always have a bad coil that may do the same thing.  Best of luck on your project.