Small Engines (Lawn Mowers, etc.): My craftsman still wont start after many replacements, overhead valve engine, recoil starter

Question
I have a Craftsman 6.75 horsepower 22" Rear Discharge Power Propelled Rotary Lawn Mower, Model No. 917.377593.  I have had it for a few years and I went to start it and it kind of had a pop or backfire and wouldn't start.  I had used it a week before and each week before that for some time and I had no problem.  I cleaned the carburator, but that didn't work.  So then I bought and installed a new carburator kit, put in a new spark plug, bought a new air filter, bought two new fuel lines as the old ones had a few cracks at the ends, drained all of the gas and put in fresh gas and drained the oil and put in new oil.  It still doesn't start!!  I get a pop or a backfire and that it about it.

Answer
It sounds like your flywheel key is partially sheared.  You will need to remove the recoil starter housing and remove the nut that holds the flywheel on and look in the keyway.  If its partially sheared it will give you the symptom you describe.

If this is an overhead valve engine check your valves to make sure you dont have a broken keeper or valve spring