Small Engines (Lawn Mowers, etc.): Tecumseh 12hp, craftsman model, metal shavings

Question
My neighbor gave me a Craftsman model 917.254611 rider with a 12 hp Tecumseh OHV engine.  He said it was running then just quit one day and wouldn't start after that.  I put some fuel in it and it pops back through the carburetor violently.  I've had the valve cover off and the valves seem to be operating, pulled the sump off and it looks like it's timed ok, no stripped gears or metal shavings. Pulled the head, valves look great. When you have the spark plug in, it cranks real hard like it's firing too early, (if it had a distributor, I'd retard the timing) when plug is out it cranks like mad and has good compression but I noticed that it will also suck your finger in, maybe that's normal.  Anyway, I figure if it mechanically jumped time there would be some damage inside the engine, but I don't see any.  Any thoughts?  Could it be an ignition electrical issue?  I've been a VW technician for years but this one's got me baffled.  Thanks.

Answer
Sometime the push rods will bend.  Are the valve properly gapped?

Did you check the flywheel key?  The key provides the ignition timing?  What color is the key?  If someone installed the wrong key the electrical ignition may be off.

Let me know.
Eric