RE: 4 stroke engine turnning propeller backwards
A four-stroke engine can run reversed for a short period, if fuel has flowed-back into the muffler; or for extended periods, if the fuel-tank vent is submerged in fuel; thus allowing the muffler to behave like a 'makeshift carburettor'...
If this is the case, the engine will be able to reach pretty high RPM... the carburettor's barrel will act as an 'exhaust-throttle'...