I have found that by using gas with no ethanol my small engines such as string trimmers and chainsaws have run noticeably better. Most premiums have no ethanol, but there is a website that will tell you where to get no ethanol gas in your area. The running problems I have had are exactly what you describe. I don't think it has anything to do with octane, and everything to do with alcohol in the gas.

Gasahol ate the fuel lines in the tank of my trimmer. Probably fine particles from these messed with the carb. After replacing fuel lines blowing out the carb and running a couple of tanks of real gas/oil mix the trimmer runs correctly.

The very FIRST thing I do whenever I buy a new small-engine implement is rip out the @#$%^&*! spark arrestor. It's a little screen over the muffler exhaust port that will clog up with gunk after a couple hours of running any 2-cycle engine. The back pressure will then make the engine run like crap and be difficult or impossible to start cold.

The @#$%^&*! government requires spark arrestors on any small engine regardless of where it's sold or whether or not it's needed, so dealers will not remove them, but it's no trick to do it yourself in most cases.

I make gasoline for a living working on a FCCU unit in a refinery, I also blend it into a final product before it goes on the pipeline, that man is
BSing you.