Decompression on a moped is achieved when you pull the decompression lever, opening a valve in your engine's Combustion chamber to allow a loss of compression so the piston can move much more freely in the cylinder for easier starting of the engine. Once the piston begins moving, the decompression lever is released and compression returns to the combustion chamber, allowing the motor to start. If the decompression valve is opened while the motor is running, compression will be lost and the motor will die.

Sometimes a moped can be started without using the decompression lever, but it has been reported that when you have spark and fuel and no fire, it is strongly advised to make sure you are using the lever properly. Mopeds that have not been started for many years may have lesser compression at first, but as the engine is run again, compression can actually build to the point where the lever is necessary.

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