The engine in the video looks very similar to the SEFFLE 25HP single semi diesel I had in FMC LILY[ Now in Jem Bates boat SEVERN ] There are several ways to stop it over speeding It is total loss oil system so if you have the snifter valve on the crankcase cracked open [& a tube& catch tank] there will be very little lubricating oil left in the crankcase for it to consume. there was also an on/off valve on the inlet side of the fuel pump. Also you see in the video before the atempt to start, the guy pumping a lever near the top of the crankcase, if you hold this lever down the pump will not deliver fuel to the injector. You can also cover the air valves on the crankcase with rag to cut off the air supply.The No 2 guy only blocked off 1 ,there is a second one under the silencer I think the problem they had was they pumped in to much fuel before starting & it had, with being a 2 stroke, fuel had drained down into the crankcase, so even if they shut off the fuel supply it would still have some in the bottom end to push up the transfer ports + they only blocked off half the air supply. The engine doing the jig couldn`t have helped much either.