CDI ignition unit NARAKU Racing, without rev limter, GY6 XL50QT-B

CDI and coil

The CDI (for Capacitor Discharger Ignition) and the ignition coil are an essential part of the ignition. While the coil is actually just an energy storage device that supplies the ignition spark to the spark plug, the CDI module is a more complex component that controls the engine speed at which the spark should occur. It can therefore have an effect on engine behavior and performance.

Open CDI

Many riders equip their 50cc geared mopeds and scooters with open, i.e. derestricted CDIs. In most cases, the original CDI throttles the maximum achievable engine speed, which significantly reduces performance and top speed.
To remove this rev limiter and thus increase maximum speed, you can install a CDI without a rev limiter instead of the original CDI.

Beware! When using an open CDI, the carburetor must be readjusted, so it is best to order new jets as well.

Programmable CDI

Programmable CDI control units are available for tuned racing engines on 50cc scooters and moorcycles as well as for motocross bikes. These CDIs are designed for more experienced tuners who want to optimize the settings of their two-wheeler as much as possible.
With a programmable CDI, the ignition timing is dynamic so that the spark always jumps at the optimum time at both high and low engine speeds. This leads to a better increase in speed, higher torque and an overall increase in maximum power.

4-stroke engines with fuel injection are equipped with an ECU (Electronic Control Unit), which also controls the fuel injection. When tuning a four-stroke engine with an electronic injection system, a programmable CDI is therefore an absolute must in order to avoid breakdowns and engine damage.

Symptoms of a defective coil or CDI

If these two elements fail, the symptoms are usually very easy to recognize: no spark at the spark plug, so the engine will not start.

It is best to proceed in sequence: First change the spark plug, then the spark plug cap, then the coil and only then consider the CDI or the ignition itself as the source.