Re: 1963 Evinrude 18 HP Ignition Question
Whoa!!! All electricity, in order to do any work, has to flow in a circuit from source to load, and back to source.
In the case of your magneto, that circuit is from the secondary winding of the coil, through the wire to the plug, across the plug's spark gap to ground (cylinder head), through the head and block/crankcase, to the magneto's armature plate, and finally through the coil's ground lead, to the secondary winding of the coil. So, you see it is a complete circuit (circle) from the coil's secondary winding to load (spark gap), back to secondary winding. To prove all this is true, if you were to remove the spark plug and connect the wire to it, but just leave the plug hanging in air, there would be no spark across the gap---because the circuit back to the coil is broken.
That metal-to-metal contact where the armature plate swivels on the crankcase neck is one of the connections in that circuit. Normally, that contact is good enough that there is no sparking. But even if it is not, the voltage across it is the same as the voltage across the spark plug gap and will jump across any resistance in the contact with ease----the sparking you see in the dark.
There is a cure for it. Don't look at it in the dark.
Now, after writing all this, I am assuming you are talking about where the armature plate rotates back and forth on the crankcase. If you are talking about arcing from a wire to the armature plate, that is a whole different ball game and needs to be fixed by replacing the wire.
