needs a bigger motor. thats a 125 coming on powerband. haha. nah, sounds like a fouled spark plug or clean out carby.
it could be low on compression. have you checked the piston and rings.

does it do it all the time or when you give it a good squirt does it get better, or remain the same.

go the ktm. my brother-in-law has the same bike but an 06 model. good fun.