If the spark plug is not firing, or you are getting a weak spark, the problem is electrical. Since you already replaced the CDI unit, you know the CDI unit isn't causing the problem. You were wise to replace the spark plug. If a new spark plug doesn't rectify the problem, you either have a bad ignition coil, or a bad stator/pickup coil.
Spud
__________________
Spud
"Never argue with an idiot. He will drag you down to his level, and beat you with experience."
Mark Twain
2015 Zongshen ZS250GY-3 (RX3)
2006 Zongshen ZS200GY-2 (Sierra 200)
2005 Honda XR650L
2004 Honda CRF250X
1998 Kawasaki KDX220
Mods made to my Zongshen ZS200GY-2:
http://www.chinariders.net/showthread.php?t=6894