I have used Amsoil 2 stroke at 100:1 for decades. This has served me well in all sorts of Stihl equipment from pole saws to string trimmers. I always use the highest octane fuel that I can find. None of my engines have locked up or worn out prematurely. My string trimmers were used for hours on a daily basis. My chainsaws are lightly used through the summer mostly for tree trimming. In winter heavy use cutting firewood and hedge for fenceposts. My secret is......keep the airfilter clean, run 91 octane fuel, a little seafoam in the fuel once a month, and a piston soak with carb cleaner once a season to remove carbon from the rings.