HRL:
Here are some questions that in an oblique way will concern old truck enthusiasts despite the motorcycle flavor of my questions.
So, do resistor plugs create a higher voltage at the plug gap with an auto-transformer type ignition coil? Or are they just current limiting? Would resistor plugs produce more voltage in the secondary winding of an auto-transformer and reflect a higher voltage into the primary winding? If so, would resistor plugs cause a higher voltage within a primary winding and consequently across the capacitor?
I know it's been many, many years since automobiles had magnetos but my '60 Matchless single and '65 Norton twin both have magnetos. One has to kick start them so it's important that they start on the first or second kick. I've seen schematics of Lucas motorcycle magnetos and they appear to be wired as an auto-transformer. The books for both say plug gap 0.020" for the magneto models and 0.035 for the Kettering (battery and coil) models. I have assumed that magnetos at kick-start RPM don't put out much voltage, hence the narrow gap. That may not be true and I've never experimented with a wider gap.
My inquiring mind would like to know because I just replaced the capacitor in one Lucas magneto, which involves dismantling the armature and pressing it back together with no more than 0.002-5" run-out. It's tedious, time consuming and i don't want to do it again soon because of using a resistor plug.
The original condenser (ca. 1960) I believe died from old age, being an electrolytic capacitor. In the 90s I worked in a motorcycle shop specializing in vintage bikes and dealt with the magneto issue many times. I tested many NOS magneto condensers still in Lucas boxes and discarded them as failed. These are of an electrolytic design and are believed to fail from disuse. Are automotive condensers (capacitors) electrolytic? Are NOS ones suspect? I have encountered many more failed new condensers fresh from the FLAPS than failed in-service condensers.
