Mentioned elsewhere in this thread (and Sailnet) is the fact that alcohol (the 15% of E85) eats rubber. (try this experiment at home - pour some isopropyl alcohol into a dish, put a peice of black rubber - say a peice of an old windshield washer into the dish, let stand for 12 hours. Do you see any change in the rubber?)
The problem with this motor is most likeley that some rubber in the fuel supply (gasket, fuel or vacuum line) has partially dissolved and is either gumming up the carb, or causing a vacuum leak.
The FIX is to identify the damaged rubber component(s) and REPLACE it(them) - preferably with a like component that is not affected by alcohol. Rub a Q-Tip over suspect parts. If the cotton turns black, or gets little gooey black blobs on it, then you've found a problem. Then clean the rest of the fuel system (needle valve seats, venturi, jets, etc.).
The best preventitive measure is to run the motor dry, but then you may have to worry about corrosion. If this is a concern, then spray a can of motor fog into the carb before storing it.