How does a motorcycle ignition system work?


Quick Answer

The mechanics of a motorcycle ignition system depend upon its type and age. Motorbikes built before the late 1970s usually feature mechanically-controlled cam-driven points, whereas post-1970s bikes almost always contain pulsar coils instead.

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Full Answer

Pre-1970 motorcycles commonly contain mechanical advance ignition systems, which work via cam-driven points. When the points are closed, electricity flows into and charges the ignition coil. When the points are open, the charge in the ignition coil flows out rapidly, sending a large amount of current to the spark plug, thus causing the engine to start.

The concept of a point-centric ignition system is very simple and has been around almost as long as the motor vehicle. However, the points do need to be replaced periodically, as they get worn out over time. Timing is handled via a mechanical advance system, which controls when the points open to produce the correct charge.

Post-1970 motorbikes usually use a capacitor discharge, or thyristor ignition system. Instead of a set of points, the CDI ignition uses electrical current from the motorcycle's battery or stator to charge a capacitor unit. The charge in the capacitor unit is then sent through the coil, where it creates the spark necessary to start the bike's engine.

Timing in CDI ignition systems is controlled by a combination of a pulsar coil component and a flywheel, which operates in tandem to ensure that the correct charge emerges from the capacitor unit at the correct time.

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