[BusNit]

There should be a mechanical fuel rack that is held by a 12v solenoid. If it cranks but won't start, he can try cranking it and manually holding the solenoid to see if it will stay running. Once that part is over then the next will be to see if the solenoid is getting power and if it is perhaps the solenoid needs replacing. If it does run but won't shut off, he would have to pull on the rack solenoid to stop the fuel and the generator will shut down.

These are my simple quick checks. (Of course there's fuel filters and the like to check too)