Curious,
Did you try a different tank yet? like the stowaway tank method? I have read all the posts. Yes ethanol is not a good thing (But) Read on
I do not want to jinx myself, but I have burnt over 5 gallons of Opti II 2 stroke oil since last August so that means I have burnt a bunch of gas. I have done this for a lot of years too. I burn premium pump gas from any old gas station. I am sure there is some ethanol in it. To be honest I do not look. But the key is in not letting the fuel sit in the tank for long periods of time. Ethanol is hydroscopic so it absorbs water and that is where the contaminant bonds with the ethanol and can produce some funk. If you can get your problem to happen again, a separate tank will tell you where the problem is. If you plug in the stow away and the problem goes away, the problem is with your tank. If you plug in the stow away and the problem is still there, the problem is between your tank connection and the engine. I made my living doing similar things mechanically for a lot of years. Now I just teach it. And run my boat and go fishing..