What ethanol does is a bunch of things;
First, it is a solvent that will eat many rubber compounds. It turns pliable rubber in your carb gasket, or fuel line, or needle valve into a sticky goo. This goo can travel through your fuel system and clog the jet. To solve this, you can replace any rubber parts that are prone to alcohol degredation with different rubber compounds which are not. It'll probably cost less than $50 in parts.
Second, because it's a solvent, it can loosen other gunk that has been hiding in the fuel system. This gunk, now set free, travels through the fuel system and gets stuck in the narrowest of spaces, kind of like a blood clot causes a heart attack. The narrowest spot in the fuel system is the idle jet. Adding an in-line fuel filter can help address this problem.
Third, while oil and water don't mix, alcohol and water do. Because of the high humidity ever present in boating this can be a real problem. This water can cause corrosion anywhere in the fuel system. The solution to this is at the end of the day to not shut the motor down with the kill switch, but cut the fuel (shutoff) and run the engine until it stalls.
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USCG Licensed OUPV Captain, ASA 101/103/104/105 Certified Instructor - Also certified in Recreational Marine Electrical Systems