As it looks like a governor problem you could try........
Disconnect everything except the water pump, start the genny and then use a bit of string, baling wire or bootlace to manually get the revs into the correct zone and stay there.
As it's a constant load it should stay wherever you leave it, with a bit of luck whatever is stuck could well free up with the warmth and vibration, should you be that lucky the motor shouldn't overspeed, the governor ought to shut it down.
Anyway, if you stand by it for half an hour or so you'll have moved some water in the right direction whilst Bob continues with the non bush engineering side of the problem!!
Cheers
Stef