Welcome overlander!
With the experience I've had with that engine, I'd say one or both of the valves are too tight. Setting valves is quite simple on these engines:
http://hondacg125.awardspace.com/valve_clearance.htm Even if the valves aren't the problem, it's good to know how to set them properly.
Trailbikeryder, thanks for telling us about the FTR223; I was unfamiliar with that model, and I didn't realize that Honda produced the CG-style engine beyond 125cc.