I know you said you used ethanol free, but gas in general is shit these days, if the can isn't sealed well you'll still draw moisture and condensation, which still effects non ethanol gas ( just not as quickly)
the oil mix helps keep it fresh longer, but again, an unsealed can... ( the old non safety cans aren't sealed well, but sure are nice to NOT have to deal with nanny safety features )
My fix for my Stihl FS56 string trimmer was to start using the "Tru Fuel" quart cans, it's more expensive ($5.99 @ TSC ) than mixing your own, but good golly does the trimmer run SO much better ALL the time. even sitting over the winter, 5 hits on the primer, full choke, it started and ran with no issues. its NEVER done that over a winter lay down with regular 50:1 mix gas.
same every time, runs well, smells awesome ( racing gas ) and I find I don't have to run the trimmer as hard as I used too, which uses less fuel, and string. so there is a positive trade off for the cost and I don't have to tear it down, and clean it every year, which makes it even more with the cost. I'm still using a can I bought last year, have 2 more waiting that I just bought last week and I expect that they'll last me all summer ( I've got 2 yards to mow currently so this may or may not be the case )
I used the Tru Fuel to start my Lawnboy that has been unused for the last 6-7 years, added a little more oil to it ( Lawnboy is 32:1) once the LB hit it ran very well. I doubt I'll run the LB on this though as it's only available in 40:1 and 50:1 mix. I did just mix 2 gal of no ethanol 91 with some LB oil I still had, so we'll see how that lasts over the summer. New safety can and all.
