Are you saying you replaced the spark plug with a known good plug?
Ever thought that it might be a bad plug? Always test with a known good plug. New don't always means good when to spark plugs. Beside the NGK CMR6H are bad to fail in the first place. It is one the plugs that I am constantly having to replace here. Usually shorting themselves out. I have had to be bad right out of box. I even had one to cause a HS56 Hedger to diesel that local Stihl dealer tech couldn't find the problem of the run away engine.
Also try leaving the kill off the coil as there might be short in the wiring or defective kill switch.
