CDI - Capacitor Discharge Ignition
A CDI is a type of electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds (for small engines, racing engines and rotary engines). The capacitive-discharge ignition uses capacitor discharge current output to fire the spark plugs.
Many times if you do not have spark it is due to a faulty CDI module. CDI Modules come in AC (Alternating Current) and DC (Direct Current).
AC or DC?
Most engines generate alternating current to power lights, accessories, and to provide the necessary spark for the engine to run. If your engine was built prior to 2008 the odds are good it requires an AC CDI. A DC CDI is wired to the scooter's battery and uses the 12 V +/- drawn from the battery to supply the voltage for spark.
In order to get the proper replacement CDI you need to determine if you have an AC CDI or a DC CDI. A standard direct replacement AC CDI will be smaller in size than a DC CDI, measurement specs are listed for each of our part numbers. DC CDI's are larger because they contain a DC to AC transformer.
Another way to figure out the type of CDI your scooter needs is to check for voltage at the CDI. Turn the scooter key to the "On" position and, using a test meter or test light, check if there is current at the CDI. If there is 12 V at the CDI it is a DC CDI, if there is no voltage at the CDI it is an AC CDI. This is assuming the battery is charged, of course.