Low fuel costs and increased mobility through congested areas have made scooters a popular choice of vehicle for many road users. Some factory-built scooters are restricted during the manufacturing process to help reduce speeds. This means that a 50cc model, for example, may only be capable of achieving a 30mph maximum speed. With a moderate amount of mechanical knowledge, a scooter can be easily souped-up. However, users should be advised that modifications to increase speed are considered illegal in some countries.
Disassemble the engine of the scooter until the carburetor can be removed. Carry out a visual check of the carburetor for signs of a washer or ring fitted into the fuel chamber. The washer or ring is fitted to stop the flow for fuel through the carburetor and, when further restrictions are made to the air and exhaust flow, this slows down the maximum potential speed of the scooter. Knock the washer or ring out by placing a flat-headed screwdriver against the lip and tapping down gently with a rubber mallet.
Grip the jets of the carburetor firmly, using a pair of pliers. Twist the jets counter-clockwise until they are completely removed. Use a drill fitted with a small bit to bore through the top of each jet to increase the size of the hole. Screw the jets back into the carburetor, tightening them firmly with the pliers.
Remove the cylinder barrel and take it to an automotive repair shop. Ask to have the bore of the barrel widened. Buy an appropriately-sized piston to fit the new diameter of the barrel and replace the one that's currently on the end of the connecting rod. Reassemble the cylinder assembly, using Circlip pliers to ensure that the piston rings are not damaged when the barrel is being refitted.
Remove the exhaust from the scooter and use a half-inch hole saw to bore through the outlet. Continue drilling until resistance is met from the baffle. Keep the drill in a central position and apply additional pressure to force your way through the baffle. Some exhaust systems have more than one baffle so you may need to continue drilling through until no further resistance is felt.
Refit the exhaust and the carburetor before assembling the rest of the engine together. Check oil and fuel levels before starting the scooter and taking it on a test run. Remember that a new piston and barrel re-bore will need to be run-in and failure to do so may damage the engine. The maximum speed of the scooter should now be increased as much as 100 percent.
