The CDI, short for Capacitor Discharge Ignition, is an electronic control module that controls the ignition timing of the spark plug and thus the entire combustion process. The main two types are static CDIs with fixed ignition timing and dynamic CDIs with variable ignition timing, in this type of CDI the ignition timing is dependent on engine speed. ... For performance enhancing purposes, the ignition timing of 2-stroke engines is often delayed a little bit to optimize combustion. For 4-stroke engines, a slight advance can optimize performance. In addition, by installing an open, derestricted CDI you can also override the rev limiter, or derestrict tuned scooters via the CDI. In our shop we carry both static CDIs and tuning CDIs with variable ignition timing. We feature manufacturers like Polini and Naraku and of course Malossi with their Digitronic and Force Master series.