Hello can anyone help me i have bought an Aprilia RS 50 that doesnt rev right it revs to 6500 rpm then splutters. The man i got it off said he was riding down the road to work 1 day at 65mph then it just seemed to slow down and not rev past 6500 rpm. Ive rebuilt the engine but it still doesnt rev some times it will rev about 1 time out of 10 it will work, does anyone know what the problem could be as its really got me in a rut thanks for any help