I agree with you, that's the way to get spark out of the secondary of the
ignition coil. (I was playing with that stuff in first grade! My parents
figured that with just a lantern battery and some old car and radio parts I
couldn't do anything dangerous... It wasn't until junior high that
I discovered car radios with working vibrators, and by that point I
had figured out TV flybacks.) IIRC having a bad
capacitor also ate the points. (I think when I was a kid an old rasp
and a dragged wire often served as the points after I destroyed the
originals.)
But electrically, what does that capacitor do? Does it
make a tank circuit on the primary such that it doesn't spark there,
so it has to spark on the secondary? The capacitor will limit dI/dt
which will potentially limit the spark if it's too big, though I guess
it's more important for the spark to come out of the right place
In the perfect world, where the two windings were 100% coupled,
resonating one would resonate the other, but I would guess that the
coupling in an ignition transformer is way less than 100%. Am I anywhere
near the proper theory?
Tim.