Here's what Stihl says about ethanol and octane:
https://www.stihlusa.com/information/articles/gasoline-guidelines-outdoor-power-equipment/The ethanol thing always causes a fuss amongst small engine users and boaters. Usually it falls out with folks from the Northeast and West saying it makes no difference and folks from the South saying it's the devil. I know that my engine problems went down by orders of magnitude when I swore off of ethanol fuel for my small engines and my boat. In my vehicles I burn the cheapest stuff I can find, usually 10% ethanol 87 octane. The difference in the South is our humidity, we've got a lot more than other parts of the country. Ethanol fuel reacts badly with humidity, it absorbs more moisture from the air down here. Ethanol fuel doesn't store well down here for that reason. For a fuel injected engine I don't think it makes a whole lot of difference, especially in vehicles where the fuel is burned in a matter of days instead of sitting in the tank months at a times. My boat has a fuel injected four stroke and I could probably get away with E10 in it even though I don't use it that much. I just like the extra peace of mine with non-ethanol although I'm fine with using 87 octane. For anything with a carburetor though I'm adamant that nothing other than non-ethanol will touch mine. Chainsaws, weedeaters, ATV's, etc. If it's got a carb I'm not putting ethanol fuel in it, I've had too much trouble over the years from it. It degrades too quickly in my environment and I've replaced or rebuilt too many carburetors from it. The higher octane stuff is a no-brainer in small two strokes, the price difference is insignificant.
Bottom line, use high quality fresh gas in your small engines. Put the crap stuff in your car or truck, they'll run off of anything.
