Onan Generator Hunts Under Load

There are separate fuel pumps. The vehicle and the generator each have their own. If you suspect a fuel issue, try running with a load when using the external fuel can. I don't think the fuel is at fault. When you replaced the carburetor, did you make sure the linkages and springs all ended up in the correct holes? I seems like the governor is making too big of an adjustment and once it starts oscillating it can't stop. Try turning the sensitivity down before the next load test.