If things are really bad, there's no getting around pulling the carb, squirting the jets, main and pilot, out with carb cleaner. Let sit, more carb cleaner, then blow out with an air hose.
Another option, drain fuel bowl, close up, pull the intake fuel line, top of the carb float bowl, and fill up with Sea Foam. With switch off, and carb choked, pull the starter handle 3x, to fill the jets with Sea Foam. Let sit 48 hours. Fill fuel tank with fresh fuel with 2oz of sea foam per gallon, start up in Eco mode and let run for 5 minutes in eco mode with no load on the generator.
If it runs right, the Sea Foam got all the varnish out of the jets, if not, time to tear down the carb, or just buy a new main jet and replace it. Soak the old main jet in carb cleaner until it is possibly usable again.
