After removing valve cover is top valve the exhaust valve. Engine spins fine with spark plug removed. With plug installed engine rotates to a hard spot and prevents proper rotation for starting.
This problem is caused by excessive valve clearance on the INLET valve. This prevents the compression release from working, making the engine difficult or impossible to crank. From memory, I can't remember which one is inlet, but the EXHAUST is the one that opens first AFTER compression.
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