Wasted spark system

The remaining coil energy is available to fire the spark plug in the cylinder on its compression stroke (typically about 8 to 12 kV).

[2] This significantly improves reliability, since many problems with a conventional system are caused by the distributor being affected by dampness from rain or condensation, dirt accumulation, and degradation of insulating materials with time.

Most single cylinder [four-stroke] engines use the wasted spark system in order to capitalise on the simplicity and reliability of the flywheel magneto.

These engines need a flywheel to run smoothly, and the heavy current-generating magnets help provide the momentum while delivering a zero-maintenance drive to the ignition system.

Mounted directly on the end of the crankshaft, all the stress that spark generation would otherwise place on the camshaft chain (or another special purpose half-speed drive) is avoided, while there is virtually none of the strain that necessarily degrades the ignition timing in systems relying on chains or gears.

In modern conditions, this method has a very small impact on the length on the service intervals of the vehicle and the longevity of individual components.

Reasons for this include reliability (especially as a failsafe in aircraft engines), for improved starting, and for better combustion performance by initiating the flamefront at opposing points simultaneously (e.g. Alfa Romeo).