Welcome Bob! 
Maybe the spark is coming at the wrong time in the cycle?
(Sheared flywheel key)
Does the engine seem to be pumping the usual amount of air? Can you feel suction on the carb and any exhaust air movement while cranking?
(Broken valve or piston connecting rod)
Maybe the spark is coming at the wrong time in the cycle?
(Sheared flywheel key)
Does the engine seem to be pumping the usual amount of air? Can you feel suction on the carb and any exhaust air movement while cranking?
(Broken valve or piston connecting rod)