Re: shocked
Try running your motor at night to see if you can see electrical arcing anywhere along spark plug wires. You will not, of course, be able to see anything from the point where they pass through the armature plate into the area under the flywheel, but you might get lucky and see something from that point to the spark plugs.
A couple of possibilities that come to mind if you just replaced your spark plug wires, are the rubber grommet that goes on the end of the wires, at the coils, and the high tension lead clamp that holds the wires in place against the bottom of the armature plate. You could be getting leakage at the coils if the grommets weren't installed, and you may have pinched one or both of the wires at the clamp.
I think Steve's point about armature plate movement is a good one too. As you are looking for the source of this problem, advance and retard the throttle a little to see if it helps in finding it.
