I have a 1965 Honda S65 that has an electrical problem. When the ignition switch is in position #1 (lights off) the bike idles and runs fine. When the switch is moved to position #2 (lights on) the headlight and tail light come on but the engine immediately starts to cut-out both at idle and when you try to speed it up. Neither of the bulbs blows out. When switched back to position #1, the engine immediately runs fine again. I have done research and know that it is a magneto ignition system and therefore does not need the battery to start and run. However a battery needs to be installed because it acts as a voltage regulator. The battery is charged from a lighting coil. That is shunted for running without lights. When the lights are on all the windings are used for extra charging capacity to keep up with the load on the battery. I have been told that the headlight, tail light and instrument panel light run on AC from the lighting coil. The horn, neutral light and stop light are DC and are powered directly from the battery.
My theory is that the problem is a bad lighting coil. I suspect it can not handle the additional load when the lights are switched on. However, I am not certain why this effects the running performance of the engine. I am looking for someone with knowledge of these systems to confirm my theory or give more more insight as to what might be going on.
