All I'm going to say is if you decide to disconnect the governor, remove the small gear inside. They could break and come apart at high speed and that would damage the motor.
If I understand correctly you are trying to run a 72 on the motor, 13 on the jack shaft, 13 on the jack shaft and 72 on the wheel. That's a 1:1 ratio. That will never work. You need about a 6 to 7:1 ratio.
The only way for your piston to hit the valve was for your timing to be incorrect.
Or the motor was rev'd to a point where the valves would float. Which would be corrected by changing the valve springs for stronger ones.
The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. You can use a higher octane fuel in a low compression ratio motor but not the other way round. If you do the motor would knock.
I rap a tie-down strap around the flywheel in the opposite direction of the nut you are trying to remove and securely fasten both end of the strap to your work bench. As you put force on the nut the strap tightens around the flywheel.
pete
take the cover the flywheel and check it out. the ones i've seen have a band that rubs against the flywheel to stop the motor when you release the safety hand/level.
pete