According to Eigenvector :
Premium gas has small amounts of ethanol to help clean deposits as well a
absorb water in the tank. It isn't CLEANER gas by no stretch of the
imagination - it's all clean. It might burn cleaner, but this isn't a car,
its a trimmer that doesn't have a catalytic converter nor a complicated
exhaust system.

And probably dumping partially burned 2-stroke engine oil out the muffler.

Ordinary ethanol blend fuels have the same octane ratings as regular,
and usually cost about the same. The ethanol they have is a lot more
than "a small amount" (I think they can be up to 15%).
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.