Norm, I just had the same problem with a PT I picked up ($8 at the tip). Anyway, I have since worked out it's quite rumbley in the bearing department.
Rebuilt carb, and fired after 3 pulls, ran 5 seconds and stalled. Tried another plug, nothing. New screw in the plug wire, nothing. Another new plug and it sprang to life
Funny thing is all plugs had spark outside engine
Old plug in it was light tan/brown so maybe you are onto something about straight fuel
