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.
It doesn't help when those OS plugs are shorter reach which makes it even harder to get a better combustion since the plugs element is recessed into the head by a few threads. For optimum performance, the bottom of the glow plug should be flush with the inside of the combustion chamber. Too long of a plug like the 4-stroke plugs with the protruding end in an engine designed for a standard long plug can sometimes cause problems by changing flame propagation since combustion would be taking place below the top of the combustion chamber. It also raises compression slightly. I've used an F plug in some 2-strokes and it's worked fine but the engines ran better and faster on a standard long hot plug.
The MC14 and MC4C are for 4-cycles and helicopters (the MC4C is a standard long reach plug, no protruding "nose"), MC55 and MC59 are for low and low-med nitro fuels. I venture to guess the 14 and 4C are the hottest followed by the 55 and then the 59. I liked the Enya 3 better than the MC4C in my Enya 4-strokes. Lower idle and better top rpm. The 59 didn't fair as well in the 4-strokes but did work okay. Idle rpm needed to be a little faster.