Working Principle of Ignition System: An alternating current (AC) is generated when a magnet moves between two stationary coils. In a magneto, a coil of wires moves between two magnets to produce AC. This AC supply is rectified before use. After rectification this current is also used for other electrical purposes.
The CDI unit consists of a capacitor which is charged through the AC current. When reluctor comes in front of the pulser coil a small amount of current (pulse) is sent to the CDI unit which discharges the capacitor. The discharged current flows through the primary windings of the ignition coil. This induces current in the secondary coil and the voltage is stepped up. This high voltage current jumps across the gap between spark plug electrodes and generates spark.