Talking about those engines running backward, we had a 2 cylinder John Deere tractor. If you just about were to kill it and pull the clutch it could kick back and run backwards. It did have a decompression lever and my dad told me if it happened to just push the decompression or else put it in 6th gear and slam the clutch in. Happened to me twice. Also had Ajax 1 cylinder motors that run these pumping units do it once. If the engine about died the counterweights would rock the unit back and the engine could start running backwards. Those were two cycle engines with ports and not valves and it didn't seem to hurt them to run backwards.