its a stock 250cc with 300cc top end bore kit, with jetting and modiefed stock exhuast

they didnt dyno tune it cause there dyno was broken,

they said not to go over 5k rpm in first hour of riding and i didnt, i just put 500kms on the new engine and now im starting to slowly try give it more but this is wat happens when i do..

open throttle in mid revs, = deep throaty sound and power loss,

rev to 6-8k rpm = power stops and engine splutters, exhuast blow more smoke, wont rev higher than 7.5k rpm, unless i very sloly apply small amounts of throttle, but still near to no power increase,

bike starts up mint and runs fine until around 5k rpm,

themechanics said they went froma 110 jet to a 150 or 160, and the i checked the airbox it has been drilled,

? help plz?