He says it has spark so I doubt it's the ground, I'm thinking a sheared key on the flywheel that trips the pick up if it's keyed to the shaft. That would still allow spark and everything else to work but still not start. Never inside one of those so don't know if that flywheel is on a spline or not. Also valve not closing crossed my mind but on a 3 cyl it would probably still start. Once I get some more details my opinion may change but thats what I'm thinking right now.

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