well it depends on the exhaust pipe it has on it ,if its a race type expansion chamber then it may be that the engine cannot create enough back pressure to run properly due to the gas flow of the pipe being to fast or it may just be that its only 50cc they are not very powerful and will struggle up long drawn out hills or steep hills.if it does have a race pipe then fitting some 5 gram rollers may be a solution.
adam bike doctor, April 2010