After checking spark plug terminal current with a 10 volt analog meter ,the Victa internal coil (inside flywheel) and Villiers torque major were both positive to the spark plug center electrode.
The Powertorque and side pull full crank and the mower I converted were all negative to the spark plug center electrode.
To check the voltage you have to spin the motor over as if you were starting the motor, a very slow spinning motor gives a false reading.
The mower I converted starts first time every time except if I don't prime the carby when it's been sitting for a day. Also takes very little effort on the starter to start.
Just shows you that the points coil even with a module to convert the ignition to pointless is never going to be as good as the Victa pointless coils.
The coil design will control if the plug is negative or positive.The direction in which the wire is wound around the coil. The North-South polarity of the magnet(s)
For plugs in a positive polarity position, more electrode wear will occur at the ground electrode. Plugs in a negative polarity position will experience more wear at the center electrode.
If the direction of current in the first pulse is such that the spark plug tip is negative that is better because the tip gets hot and some thermionic emission takes place assisting spark formation .The term used for this by old school Auto sparkies was "Coil Polarity "
Image below shows magneto with positive to the plugs electrode then negative to the plugs electrode .
