In the days when machines like mine were designed and built, the era of electronic ignition had not yet dawned on us, or was just about to do. Therefore, the ignition systems were quite a bit different than from today’s electronic ones.
On racing bikes it was normal to run a battery powered total loss system, meaning there was no generator or alternator to charge the battery. One would just start the race with a freshly charged battery and hope that the charge would last you through the race. Which it always did. The battery power is routed over the primary windings of the ignition coil and then over something called the breaker points. When the breaker points are closed they allow a magnetic field to be built in the ignition coil. When the breaker cam, which is usually driven by the camshaft, opens the breaker points, the magnetic field collapses and a high voltage output is produced in the coil’s secondary winding – sending 25000 volts or more to the spark plug which then ignites the air/fuel mixture in the cylinder.
The capacitor (Condenser) has two functions. Its main function is to form a series resonant circuit with the ignition coil. During resonance, energy is repeatedly transferred to the secondary side until the energy is exhausted. As a result of this resonance the duration of the spark is sustained and so implements a good flame front in the air/fuel mixture. The capacitor, by default minimizes arcing at the contacts at the point of opening. This reduces contact burning and maximizes breaker point life.