Unfortunately, this one is better left to a pro technician because of the specialized equipment necessary to diagnose it. No load and full load voltages and frequencies must be within spec for the generator to carry a rated load. You can rule out a fuel issue by inspecting the fuel line from the tank connection to the generator connection. Old rubber fuel hoses can crack and begin sucking air, which could lead to operational ills when a load is applied. You might also try running the generator from a separate fuel source, then applying the load. If it quits again, you'll know the problem is in the generator and not the fuel supply.