Impulse Coupling

An impulse coupling is a mechanical device fitted to one magneto that provides a hot, retarded spark for easier engine starting. It works by winding up a spring and releasing it rapidly to spin the magneto magnets quickly, generating a strong spark at low cranking speeds. It also retards spark timing during start to prevent dangerous kick-back from the starter.

Key Points

• •Fitted to one magneto only — not all magnetos — to aid in engine starting.
• •Retards spark timing during engine start to prevent kick-back from the starter motor.
• •Produces a strong spark despite slow cranking speed by rapidly releasing a wound spring.
• •Once the engine is running, the impulse coupling disengages and the magneto operates normally.

Related Terms