Wondering if everyone runs the generator under load for at least an hour every month as recommended by Onan and still have these problems, and use Stabil like Donc says?
Parked my rig with full fresh tank of fuel (but no Stabil)
at the end of 2019, and tried to follow the monthly generator exercise while laid up during 2020. Succeeded for several months, but got lazy early summer, missed 3 or 4 months, and when I tried to start the gen in October--crank, crank, crank, but no start. I knew what the problem would be--pulled the carb bowl--and sure enough, green pasty gunk in the bottom. Ran the fuel pump to flush the line and the E-10 gas still looked and smelled good (Ford V-10 running fine on it). I thought the problem would be with the solenoid shut off valve in the bottom of the carb bowl gunked up, but that still worked freely; the restriction was in the main jet needle that has the altitude adjustment. Pulled that apart, cleaned up the bowl and all pieces with brake cleaner, reassembled everything--fired right off and ran like a top.
I went ahead and ran all the (almost) year-old gas out of the rig, filled fresh, and added Stabil this time. Been a little more conscientious about the 4 to 6 week generator starts since then--no more problems. I did buy an extra carb to add to my on-board spares; at thirty-something bucks I chalked it up it as insurance since I've confirmed what everyone else has told me---that the problem absolutely can