What is the purpose of an impulse coupling in a magneto?

The purpose of an impulse coupling in a magneto serves a dual function that encompasses both generating high voltage and retarding the spark for starting.

To generate high voltage, the impulse coupling works by allowing the magneto to rotate freely at first, which leads to a rapid buildup of speed and energy. When the engine reaches a certain speed, the impulse coupling engages, causing the magneto to turn and induce a high voltage in the ignition system that is necessary for sparking the fuel-air mixture in the engine cylinders.

Additionally, during the starting phase of an engine, it is crucial to time the spark correctly to ensure reliable ignition. The impulse coupling retards the timing of the spark to allow the engine to turn over more easily. When the impulse coupling is engaged, the spark occurs later in the cycle, ensuring that the engine can start smoothly without backfiring or other issues that can occur if the spark occurs too early.

Together, these functions enable efficient engine operation by ensuring proper ignition timing and providing sufficient voltage for spark generation, particularly in challenging starting conditions. This intricate interaction is at the heart of why the impulse coupling is an essential component in magneto ignition systems.