What is a CDI?

Answer 1

CDI stands for Capacitor Discharge Ignition system

it is an ignition system and also filters the fuel before it enters the engine which is affective

First of all, the CDI does NOT filter the fuel -that's what the fuel filter is for! And more specifically, the CDI or Capacitor Discharge Ignition box is a small electrical device which consists of a small transformer, a charging circuit, a main capacitor, and triggering circuit. How it functions is this,

First, the transformer takes the normal 12 volts DC from your system and steps the voltage up to around 400 to 600 volts.

Then the current which has been increased, flows through the charging circuit to charge the main capacitor. Inside the charging circuit there is a rectifier which prevents the capacitor from discharging prematurely

Once the triggering circuit receives the triggering signal from the stator, the triggering circuit temporarily stops the charging circuit, allowing the capacitor to discharge it's stored energy very rapidly to the ignition coil.

Then the ignition coil can do it's job of once again stepping up the capacitor's discharge of around 400 to 600 volts up to around 40 kV at the spark plug! Once the capacitor discharges to the ignition coil, it repeats the process again and again.

Lastly, you misused the word "affect" -you were probably meaning "effective"... learn your grammar, son!