Electric problems with my Zongshen gs250

I am having problems getting a strong/reliable spark on the Zongshen gs250 I have changed the starting coil and I have a measured amount of power coming out of the spark plug boot but no spark from the plug. If any one has had something similar happen to them please let me know or if any one has any idea. Please help

While I'm sure you have, is it the spark plug? I've had plugs in the past which look great when you hold them upside down but turn them over and the insulator slides down closing the gap or covering the end of the electrode.
Just a thought?