Well done Paul, a nice engine! - Just a "point" on the "points"... the contact deterioration (arc erosion) is caused by the reacting current from the coil causing feedback when the contacts break. This (as I guess you know, but some other readers may not?) is countered by the capacitor, so the current rushing back out of the coil rushes into the capacitor (Old car buffs call it a condenser). It's a natural current caused by the back EMF of the coil.
What we are trying to do is open the contact, so the stored energy (your 10mA rms) in the coil leaps out of the HV side across the spark plugs. But being energy that will escape every possible way, it also tries to rush back across the points from the LV side of the coil. This is the damaging current that literally "burns" the contacts... (Arc voltages cause iron molecules at over 2000 degrees C to burn in air). Steel contacts only last ~1000th of the life-time of platinum contacts (as on the Contact Breakers bought in the car spares shop). But if you polish off the arcing oxides from your steel contacts after each run I'm sure you'll manage. (I had a magneto on a Bike back in the 1970s with contacts that had had the platinum filed off by the previous owner. - I ran it on my bike, but cleaned the points every 200miles, or tank of fuel, until I managed to buy some new (maintenance free) parts.
But now you'll tell me the Minimag MIC1A control does the "heavy current switching" - and you are right. I was thinking of simple "old-fashioned" non-electronic systems. (These electronic things were only invented in the 1970s, after my troubles with old, knackered bits!).
N.B. On "non-electronic" systems, If the capacitor fails, the points will burn incredibly quickly and you won't get many sparks at the spark plugs, as they will all be across the contact breaker points. (Been there, had that!). I have also had a distributor cap that had worn (arc eroded) so much that the sparks could not get across the gap to get to the spark plugs! A new cap and rotor arm (Measurably better!) sorted that unreliability. (My temporary fix was a thick bead of solder on the rotor arm contact. That got me to work nicely, without the previous mis-fires, until the new parts arrived). Ever wondered what the black dust is that collects in distributor caps? Or inside contact breaker chambers? (Sorry, stupid question, no-one does that!) - It is the vaporised metal from the contact arcs. - Being metallic oxides it also encourages flash-over inside distributor caps, from the high spark voltage there. So "Clean Caps" are best!
Hope my attempts at not "talking in electrical terms" helped some understand this? I can explain impedance, leading and trailing voltages and currents, but it confuses some non-electrical people.
K2
