Problem solved guys. After much binding in the marsh, and checking all the usual suspects with no success, it turned out that the Mitsubishi has a fine mesh screen in the muffler outlet that was almost completely blocked. After about 4 revolutions enough back pressure had built up in the muffler to stop the engine but it would bleed off enough to start it again straight away and run for another 4 revs. Now the weird thing is that I know for a fact that the generator had been running perfectly the day before it decided it wasn't going to go any more. How it blocked up in a matter of a few hours is still a puzzle. Pulled the muffler off and cleaned the screen and it is now running perfectly again.
