That is the trouble Evolutions have with OS 8 range plugs, they load up quickly and have a hard time burning off the fuel. They can be very hard to throttle up after cranking. I had to nurse the throttle up, ease off, nudge it up some more, etc until it finally would run. You can tune a lot of that out with a meticulously set low speed needle, which you need to do anyway. But, it still needs a hotter plug. I'm going to try a MC 59 the next time I see one. I'm slowly getting away from 2 strokes.