gilera 50cc 2001 very sluggish and judders if revs are to high???

always had problems with my gilera spend loadsa money on it but judders if i rev it too high plus its really sluggish. just put gianelli pipe mallossi variator and rollers and kevlar belt on it and i can tell it wants to go faster but finds it hard to speed up. been told its somthing to do with the coil or electrics anyone know?