You might have the carb to lean richin the high end and the low end and try that. If your getting that good of a spark it should crank unless your not getting enuff fuel. I ran my weedy motor today on my plane and it has EI on it and it would not hardly crank,so i riched the carb and it cranked up. I then had to richin it up about a half a turn to get it to turn up some rpm's. I then tryed to fly it when it all went wrong. I forgot i was on the wrong model in my futaba 9c radio when i pulled up it was fine but when i went to make a fast turn she rolled over and hit the ground. It did not hurt the fuse but it did break the sheating on the top of the wing but i can fix that so i guess it was not to bad. It was my own dumbness. You win some you lose some.

Thanks
smallplanes