Misfire at idle, goes away under load but will start to sputter after a while

[lahren68 6]

Got home from work and pulled the tin shields off of the engine. I began inspecting the pickup coil and flywheel. It looks like the raised portion on the flywheel has been damaged at some point

[pfrederi 19,919]

That isn't a good thing but there is enough that it fires the plug  at least a lot of the time ..I don't see directly why operating temp impacts the issue...and why choking it helps???  

 

Spark check while it is acting up will be the ultimate test.

 

By the way Breakerless are like a magneto system.  The do not need a battery.  Never ever put 12 volts to the coil as you might do while testing a Battery points system.  it will fry the trigger.