50cc mopeds have a restriction placed on how fast they can drive, which helps keep smaller moped from travelling too fast for its size. However, it is possible to remove the restriction to gain more speed. Though this process varies slightly from model to model, the type of restriction also varies from a muffler restriction, a carburettor restriction or a transmission restriction. The general process is the same for each restriction, but part placement will vary depending on your moped model.
Look down your muffler pipe to determine whether it is restricted. A restricted muffler pipe will be gradually become more narrower along its length.
Unscrew the screws holding the head pipe of your muffler. Place this restricted pipe to the side.
Screw the unrestricted muffler pipe where your restricted pipe used to be. Tighten the screws in evenly, being careful not to screw one in too tightly before the others are finished.
Unscrew the air filter and remove it from your engine. Place your new air filter in place and screw it down.
Test your engine to see how well it runs. If your muffler is too loud or the engine runs awkwardly, you may need to double-check your work.
Find your carburettor and unscrew all the screws holding it in place. Carefully remove any belts that may be attached to the carburettor using the correct size wrench. The size will vary depending on your model. Take the carburettor out of your engine.
Open the carburettor and inspect the main jet. Remove the main jet by unscrewing it from its holding. Place a smaller jet inside of the carburettor.
Screw the carburettor back into place. Replace all belts using your wrench. Alternately, you can avoid replacing the jet by simply replacing your restricted carburettor with a larger, custom carburettor bought at a local moped shop.
Ride your moped to make sure the engine is running properly.
Find your transmission and remove the cover. Remove the nut holding the cover to the variator assembly.
Pull your variator assembly off of your transmission.
Remove the screws holding the variator assembly in place and carefully pull the two halves of it apart. Don't remove any parts from the assembly or let any of them move.
Locate the pulley inside of the variator assembly. Find the washer in the pulley and remove it.
Screw the variator back together and place it back in your transmission. Screw the transmission cover back into place.
Turn on your engine and ride your moped to make sure it is running smoothly.