One of the most common electric scooter parts in need of replacement, the CDI module is as essential to the scooter’s ignition system as the spark plug. Touted as the brainchild of the brilliant Nikola Tesla, Capacitor Discharge Ignition (CDI) is the standard system used on most of today’s gasoline-powered scooters, as well as many motorcycles, marine outboards, and other small engines. A complete CDI module is made up of a transformer, the charging circuit, the rectifier, a capacitor and the firing circuit.
How the CDI module works
The transformer first steps up the voltage from 400 to 600 volts. Moving along the charging circuit, the electrical current charges the capacitor, and the rectifier prevents the capacitor from discharging before the ignition point. Upon receiving the activation signal, the activation circuit stops charging and allows the capacitor to discharge to the low-inductance ignition coil. This increases the original 400-600 volt capacitor discharge up to 40 kV in the secondary winding, bypassing the spark plug gap and igniting the gas/air mixture in the cylinder. The charging circuit then reconnects and resumes charging the capacitor again.
AC or DC?
Most scooters today use an alternating current (AC) system; however, the popular KYMCO scooter brand uses direct current (DC). As a result, electric scooter parts for KYMCO machines, including the CDI module, can sometimes be difficult to find.
machine size
It’s always best to match the engine size to the CDI specs. A CDI module made for a 50cc engine. maybe They work on a 100cc, 125cc, or 150cc engine, and some are designed to work on a variety of engine sizes. Others, however, will only work for a particular engine displacement. Always check the specifications to make sure you get the correct ignition parts for the scooter.
2 stroke and 4 stroke scooter ignition
2 and 4 stroke engines are completely different and as a result the ignition timing of their engines is also totally different. You can’t use a CDI made for a 2-stroke engine on a 4-stroke scooter. In contrast, you cannot use a 4-stroke scooter’s CDI on a 2-stroke scooter.
connectors
On many current CDIs, the connectors are an integral part of the unit housing, forming a plug that fits directly into the scooter’s wiring harness. On other models, the connectors may be located on cables, allowing some wiggle room on exactly where the module is mounted. The skilled mechanic can shorten or lengthen these cables as needed. The most common CDI connector style uses two plugs side by side; one 4-pin plug and one 2-pin plug. These connectors can be square, rectangular or simple spades.
Note: Photographic illustrations of many CDI connectors can be viewed on the website listed at the end of this article.
Unrestricted or restricted?
An unrestricted (or racing) CDI provides the current no matter how high the engine RPM gets. As the CDI controls the spark plug, the spark plug will continue to fire at high RPM. For reasons that should be obvious, these CDI units are made for racing use and are not well suited for regular road use. However, a restricted CDI module will stop working once the preset engine RPM is reached. Without current reaching the spark plug, the engine RPM drops below a preset limit and only then will the CDI resume supplying current to the spark plug.
When replacing a CDI module, or any other scooter ignition or electric scooter parts, it’s always a good idea to consult your owner’s manual. If the manual is lost or missing, many manufacturers and brands have downloadable manuals available on their websites.
