Initially the body of the starter is rotated while the rotating magnet remains stationary. This results in winding of the spring in the coupling. At the appropriate time the fly weights are released and the spring unwinds. The rapid movement of the magnet results in a better spark. As soon as the engine starts running, the flyweights are held in release position by centrifugal force and the magnet fires in the normal advance position. However, during engine start up the retard spark is produced when the magneto rotation is held back by the impulse starter of inertia coupling.
A spring-loaded clutch device between the engine drive and the magneto spindle that helps increase momentarily the rate of rotation of the magnet, which increases the voltage produced. An impulse starter is required while starting the engine. Also known as impulse coupling