On some machines there is a rev limiter in the cdi. However, unlike most scooters it is not a single wire going into the cdi unit. Therefore a complete new cdi unit must be purchased.

The easiest place to find them is to type in derestricted cdi on ebay and as long as its for a 50cc it should work unless its specified that it does not work fo your machine.

The next restriction is in the carburettor. Like scooters a smaller main jet is used to restrict the amount of petrol getting to the engine.

A bigger main jet needs to be used the best being jet no.90, but if you do this you must change the air fuel mixture screw accordingly and also a k&n style air filter is usually better but beware in the wet they absorb moisture and can restrict the airflow. Some companys sell socks for the filters to stop water getting in. I have never tried one of these so I cant review them sorry.

Most 50cc machines are restricted in the inlet manifold(the metal or sometimes plastic tube from the carburettor to the cylinder. A washer is placed in it to restrict the amount of fuel mixture getting into the combustion chamber. This can be simply removed however some machines have torx head bolts holding the manifold in place as a tamper proof attempt.

The fourth and final restriction I know about is the rear sprocket- this works like a push bike the bigger the faster acceleration the smaller the quicker top end but you must decide which one would be more beneficial to you. If you are constantly going uphill and are happy with a top speed of 35/40 on straights get the bigger sprocket, or if you mostly ride the flats and want a top speed of around 55 get the smaller sprocket.