Magneto

A magneto is a small generator in which permanent magnets spin past coil windings to produce electricity. On motorcycles it is used mainly for ignition: the magneto generates the high-voltage pulse for the spark plug on its own, so the engine can run with no battery at all.

Classic British bikes, many vintage machines and lots of small two-stroke off-road bikes, mopeds and garden engines use magneto ignition. On modern bikes the term is often used loosely for the flywheel alternator (stator and rotor) that also charges the battery.

Typical faults are weak magnets, a broken coil winding or a worn ignition pickup. Symptoms are a weak spark, hard starting when hot or misfiring at high revs. Check the spark first, then measure coil resistances against the service manual.