Ignition testing?

[JTT]

I've recently developed an intermittant plug fouling issue that I believe may be linked to ignition. I say ignition because carb setting are working summer settings and should actually be quite lean in these colder winter conditions. Carb has been totally down, cleaned and float level confirmed. New fuel. Clean air filter. Compression good and no indications of coolant loss.

Has anyone got info on testing coil and voltage regulator? I've got specs for the exciter and charging coil tests.