Hooman1943

Hi, i wonder if anyone could help? i have an aerox 50cc 56 plate. it is all standard except i have a malossi mhr exhaust, it flys of the spot and shows alot of power, however when reaching around 20-30 mph, it seems to loose all of its power and i am full throttling and it is just staying constantly at 20 mph.. does anyone know the problem and anyone know how i could fix this?