OK, here goes…..
FACT. Electricity follows the path of least resistance.
Fact: when time to fire, the voltage in the coil secondary starts at zero and rapidly rises until it is finds a lowest-resistance path to ground Then it arcs to ground via that path and the energy dissipates and it starts all over again till next time. Hopefully, that path of lowest resistance is through the plug wires to and across the plug gaps.
Fact: Those old mags were capable of producing possibly 50 K-volts.
Fact: The path thru the plug gaps might require only 30 K-volts to fire, or whatever, according to gap width, temperature, compression pressure, etc. So, it actually only needs 30 K-volts (or whatever) to run.
Fact: We are so programmed in our heads to look for that magical “fat blue spark”, so if it will produce that magical fat blue spark we assume everything is ok.
Fact: For whatever reason, Johnson decided to limit the coil output to something a bit over the actual voltage needed to run I suppose to protect the coils from over-volage, When built, those mags had L-shaped “teaser” brackets near the soldered connection. If the voltage is to high, the spark jumps to the teaser bracket and is dissipated. OR, if somebody has removed the teaser brackets, it looks for the next-lowest path of resistance, likely to the coil mounting screw.
Which brings us to the conclusion: If it is arcing to the screw, the voltage is way beyond what is necessary to fire the plug. The mag is ok, in fact better than it has to be, and is not broken, and doesn’t need fixing.
