gpx 250

Hi guys and gals, I just bought a gpx 250. When I hold it flat out it gets to around 10,000 rpm in first then breaks down badly back to around 7000 revs. second gear seems to rev a little bit higher but then breaks down to around 7000. if I throttle off and start again its the same. my mate rode it he's a lighter weight than me and he could find anything wrong. we rode 2 up and we couldn't find anything wrong. it's stock except for loud short mufflers. please give your opinions

Rev limiter?

Nah they rev a lot higher than 10k. Might be jetting not right for pipes.