Just goes to show how out of touch I am with motorbikes, I used to have a Kawasaki with a magneto. Air cooled the lot.
I ended up driving it into the back of a Saphire in 1992, ended up on the car's roof. hehehe.
That was the end of my oll kawalski.
Good old days, I would not mind having a bike again, but the wife will be very angry if I do.

 

A lot of small engines, especially small motorbikes, lawnmowers and outboards, use alternators and magnetos. They often use the same permanent magnets on the flywheel to generate current for the spark with one set of coils and for battery charging (via diodes) or lighting on another set of coils.

The modern magnetos don't have contacts and they use some electronic switching instead to cut the current and generate the big voltages needed for the spark, but they are still magnetos in the fact that they generate enough power for a spark from only the engine rotation in less than one turn.

Magnetos have the advantage that no battery is needed. For small engines like lawnmowers and small outboards, that is often the only electrical system fitted. On large outboards it means that even 115 hp engines can be pull started if needed (I've done that) when the battery has totally failed. On some small engines it lets the manufacturer get away with no battery regulation.

The alternators with permanent magnets have to have regulation built into the rectifiers. Car and lorry alternators have electromagnets for the field and the field current is varied to regulate the voltage.