wanabbike

rite i8 have recenlty bought a dt125 which when ridden slowly is fine. howeva when you rech 50 + it will really start to strugle to pull any more. i have served the bike new filter etc. but am runnin short on ideas now. could it be low on compresion and if so does any1 know what it should be when tested ? anyideas welcome see ya round brian