Check your valves are shimmed to spec.. I had an 05 that did something very similar, I changed the stator (which it also could be) but that's all it was were the intake valves were way too tight.
'06 TRX450ER, '03 XR400r, '04 CRF450r, '05 CRF250r, '06 CBR1000RR (StreetFighter), 07 GSX-R750, '71 CB500, '75 CL360 (Honda Scrambler), '81 Virago XV750 (the 110 Bike).
06 Black TRX450ER (Conv to kicker) "Medium" Big bore! Quikshrk (OCP), Demon, REAZ bits.