Hard starting mower

[Westmoor63]

Hello, I am working on Craftsman lawn mower 124L02 1307F1 09010758. It takes about 6 pulls to start, and usually backfires and jerks the pull rope. When it does start, it sounds like it pings for a few seconds like a car engine with over advanced spark timing. After this happens, the performance seems normal.
Would someone have any ideas why this is happening? This seems like I could be damaging the engine if I continue to use the mower in this condition.
Thank you,
Ken

 

[ILENGINE]

A partialy sheared flywheel key will effect spark timing and cause hard to start and kickback.

 

[Auto Doc's]

With this kind of issue, the first thing I verify is that the spark plug is genuine and correct for the application. Copycat/fake spark plug are a common issue these days.

The next possibility is a possible flywheel key being partially sheared because the mower hit something, but not hard enough to totally hear the key.

Last possibility is the camshaft compression relief mechanism has broken. These newer engines are built very cheaply and not made to last very long; some barely last a couple of mowing seasons.

 

[Westmoor63]

Auto Doc's,
You are correct the flywheel key is partially sheared. The flywheel puller holes are blank, no threads. I pried the flywheel upward with a large screwdriver and hit the crankshaft with a brass hammer that weighs about 2lbs, but the flywheel would not move. I will try this again.
If I drilled and tapped the puller holes, I wonder if I could damage the magnets?
Thank you for the help.
Ken