Small Engines (Lawn Mowers, etc.): Tecumseh 10 hp lawn mower engine, sears craftsman riding lawn mower, craftsman riding lawn mower

Question
An older Sears Craftsman riding lawn mower with a 10 hp vertical shaft Tecumseh I\C electric start engine; The govenor is continually hunting and it won't idle. It pops/backfires thru the exhaust as though it is running lean. I have been thru the carb several times looking for an obstruction with no luck. The gaskets and fit of the intake manifold are in good shape. the engine has good compression. I suspected that maybe the flywheel key might be sheared and thus the timing off but it is good.It runs better under load but still far from right. What am I missing?
Thanks,
Warren

Answer
Warren, this is a lean sounding running/condition....the tappet clearance or the valve seating could also be a factor, but running under load may soften this possibility.You may have to either go through the carb once more or buy a new one. Take the head off and look at the bore,,,,I wish I could help more,,,,bob