[davidpm]

Once you get it clean you many want to try some E0 gas. Some outboard repair shops sell it as do some small engine shops.
It is double the price but if you only use a couple of gal a year it is worth it.

It is often called race fuel.

 

[davidpm]

How about once you get it clean, you could use the pre-mixed shelf stuff... like this:

Gets expensive if you use gallons worth at a time of course.

Ethanol free fuel helps...

Their website says it is for air cooled motors only. I called the company and a rep said he didn't know why the website says that and would not comment on that policy.
I also sent an email and did not get a response.