hi
has the exhaust had its cone or restriction moved? i had a 50cc and put a race exhaust on but it did nothing until i was told to remove the cone then bike just done under 50mph tbh race exhaust are just noisy also try and change the rollers the exhaust should have come with a set if not phone the exhaust maker and ask what weight you will need try that
good luck
46s46
November 2008