These are paired, "wasted spark" ignition systems, meaning that when #1 plug is sparked on the compression stroke, #4 is also sparked on the exhaust stroke, a useless or "wasted" spark. When #4 is sparked on compression, #1 spark happens on exhaust stroke. Ditto the paired #'s 2 and #3.
The plugs are electrically in series. Both have to spark in order for either to spark.
Ignition high voltage can behave in unexpected ways. Not sure of the spark voltage on Mama Kaw's dual coils, but probably somewhere in the neighborhood of 20,000 to 30,000 volts. A single plug wire can test good with a meter, but it's insulation can break down when the high voltage spark pulse is generated, allowing the spark to leak to ground (usually frame) through a tiny defect in the plug wire. That would cause both paired cylinders to drop simultaneously.
Examine the plug wires very closely in good light, maybe with a little magnification.. Look for a streak of white-ish ash looking stuff or, a circular ash corona around a pinhole that may or may not be easily seen. Also, with the motor running, move the plug wires around some, concentrating on separating them from any contact with ground; the motor itself or the frame. Also, don't forget to remove the plug wires from those straps on top of the valve cover if present.
Good Ridin'
slmjim & Z1BEBE
