Switched to Ultra on my 066 last year
I would estimate close to 400 hrs on this topend,,,,in the last year flush cutting stumps, some falling and bucking, but mostly,,, flush cutting stumps with a 30 or a 36" bar The carbon stain you see in the cylinder's combustion chamber was there from the previous original piston and looks worse than it is....plus I mix @ 40:1 so its a bit thick,,,I pulled this unit down because the Clutch side seal got wiped and the saw wouldnt run on it's side,,,got to looking and the bearings were about shot also so I changed them all out plus new seals and woods ported the cylinder while I had it scattered,,,,finally Put it all back together today
even at 40 :1 it smokes a little but not bad,,,,The big plus I see is the reduction of Carbon,,,,,,!
the internals/bearings were just dripping with oil and the rings were very clean, this stuff really lubricates good,,,, (I had brought it home with a red rag over piston and crank and it soaked the oil up before I thought about pix) the Stihl tech that I'm training under,,was there when I pulled it down and he knows the abuse my work saws live under,,,,when He looked at the internals He called the store Manager over and showed it to him,,,Well they rent all sorts of two stroke equipment Concrete cutters, chain saws, string trimmers,blowers,, Including the largest hand held Brushcutter sTiHl makes 353 SG or something like that,,,they immediately switched to Ultra in all their rental stuff!!!!! when you rent a two stroker from them,,,, the ultra fuel mix comes with it,,,,,
And Thats no BS!!!!!!!!!!!!!!!!!!