Ahhh the famous CNS carb....well assuming that the problem isnt something simple like a slipping clutch ( it wouldnt bog tho) my guess would be that if you have upgraded the plug already, it a carb issue. I personally have no experiance tuning the CNS carbs, but they are notoriously finiky and tough to get right especially if its the newest version (V2).
I would start with removing the carb, dissasembling it to ensure that it is proporly assembled, and with the help of the "Carb installation and rebuild" thread on here (it is stickied in the Intake and Exhaust section I believe) proporly tune the carb. Also search CNS carb to find out how others have solved their issues as I know that there have been problems with a vaccuum line on that carb. Its hard to tell without hearing the motor "bogging" but bogging is generally caused by an improper fuel/air mix in the carb.
Check out that thread and let us know what you find, or any new symptoms.
-Dan