Once you find that 12V (or 2 6V in series) you may have solved part of the problem. The furnace, refrig, wsater pump, and possibly water heater all take 12V from the house battery. There is a good chance that old gas has accumulated in the generator. Try some Seafoam to try to clean out the jets. If that fails you could be looking at a new carburetor. Old gas lines also deteriorate to gennys so that could also be your problem. A crack in the line will let it suck air and lean out to where it won't run without the choke.
