I have had a look and this thread is the nearest I can find to what you have described:
https://www.outdoorking-forum.com.au/forum/u...ords=capacitor&Search=true#Post32369The primary purpose of the capacitor is to store the kick-back of energy as the field collapses in the coil, immediately after the points open. By doing this it enables the voltage across the coil primary to swing very quickly from say +12 Volts to -150 Volts, storing energy momentarily in the capacitor then returning it to the coil as a voltage reversal. The voltage generated by the coil is determined by the rate of change of magnetic flux in the coil's iron core. If you try to operate a conventional magneto or Kettering ignition without a capacitor, there is virtually no spark. Essentially, the iron core of the coil is magnetically saturated before the points open, and contains considerable energy. The objective of the ignition process is to convert this magnetic energy into electrical energy, and use that electrical energy to produce a strong, sustained spark across the spark plug gap.
As well as magnifying the energy input to the coil, the capacitor is accurately sized to equalise erosion and deposition of metal on the two points. If one point gradually erodes and the other builds up, you need to replace the capacitor, because the one you have is not precisely the right capacitance value.
