72 Duster, Ethanol gas, intake backfire

my lawnmower wont last 3 weeks without gumming up the carb jet. Here in the summertime, not alot grows so I dont mow all that often, but I can guarantee the first time I try and start it from a months rest, it wont start and Ill be cleaning jelly out of the tiny carb bowl. I guess the fuel system is not sealed from moisture as well as a car (although they are not sealed well either unless they are EFI, with the Holley and Carter bowl vents wide open) and I live 7 miles from the beach so its not dry weather here with every morning cloudy that burns off by 10. I have a clear bottle I store gas in. If I fill it and cap it, its clear. If I leave the cap off for an hour, it turns yellow. Hygroscopic.....the ability to absorb moisture. Dot 4 or lower brake fluid and blended gas.