Motorcycle Repair: c100 engine bench testing

Question
Bill:
I have several Cub engines and I want to test them on an engine stand I built for them. I am unsure of the wire connections to do this. Seems to me the engine should run with no battery, the battery being needed for lights and other electrical parts. Have you done this? I know the ign does not ground to the frame directly. Any suggestions?
Thanks

Answer
Lee, the engine's ignition system is self-powered magneto, so needs a ground through the ignition switch to the chassis to shut it off.

Battery is needed just for street driving, but also serves as a ballast/balance for the charging system, as there is no regulator provided, just the rectifier. The charging system can go to 20 volts on an open circuit, which is what blows out the light bulbs if you are running a complete bike with dead/no battery installed.

All you need is the wires coming out of the magneto connected to the ignition coil. Put in a switch of some kind to ground the primary side of the coil to shut it off.

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php  for diagrams.

Bill Silver