Go to Lowe's or Home Depot and get some of their pre-mixed gasoline. It's available in 40:1 and 50:1.
The base gasoline is non-ethanol premium. The stuff stays good a long time.
Me I would stick with the Stihl Motomix until the end of the warranty period.
My Stihl chainsaw is over a year old and the only fuel I've ever used is the premix stuff I get from Lowe's. Even after sitting several months in my storage container, with the gas in it, the saw fires right up within three or four pulls.
