Another Theory:  The text of the MSD warning as quoted a couple messages back 
specifically says that operation of the MSD could be disturbed by RFI, such as 
that produced by solid core wires.  This indicates that whatever control 
circuitry is in the box can get confused, and maybe it won't be making sparks 
quite the way it should. The interference wouldn't have to break anything to do 
this.  It would probably work fine away from the rpm range where the sparks 
happen at just the right time to screw up whatever important decision the 
control box is making.
Stu
 
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