gy6 engine hard to start then now won't start at all. Pulled spark plug and tested by grounding to engine and it wil fire once when it is first turned over. If you let it set for a second and try to start it again, same thing, one spark and that is all. I replaced the ignition coil but that didn't resolve the issue. Any thoughts would be appreciated. Thinking of ordering AC CDI, in hopes that is it.