the only real way to deal with this:

Is to use Non ethanol fuel.

Ethanol will work ok in cars because the system is sealed from atmosphere. In any carbureted application it won't work as well. It separates and actually causes swelling and deterioration in rubber parts in carburetors. It will cause rubber fuel lines to shed and cause passages to block.

The other alternative is to shut fuel off in an outboard and run it out of fuel.

good luck.

rich