Distruputer

Basically it prevents arcing when breaker points open up, and in electronic distributors it dampens out voltage spikes that might be picked up by the radio antenna and heard as static or popping sounds on AM. When the ignition coil fires, the capacitor gives the primary current a place to go when the magnetic field is collapsing. That collapsing magnetic field is desirable and necessary to induce the very high voltage in the secondary coil winding. Without the capacitor, the coil would not work as efficiently and spark would be weak.

Think of a capacitor as a really, really, really tiny battery. It is just two layers of tin foil with a layer of insulating paper in between all rolled up and stuffed in that metal can.

Caradiodoc