If you purchase a Boyer Electric Ignition system the manufacturer recommends that you install 6-volt coils. This recommendation is sometimes over looked. A clear reason for replacing the coils is not given. This recommendation is made even though the 12-volt coils will work. The following is the reason this recommendation:

Boyer electronic ignition Kits work best with less than 6 ohms total resistance on the primary side of the coils. Since the coils are wired in series (per instructions), the resistance is the total of all the resistance in all the ignition coils in the system (OHMs Law for you engineers). Stock 12-Volt coils have 3.5 ohms of resistance each, so a twin cylinder bike with two coils has a total resistance of seven ohms. A triple coil bike has a total resistance of 10.5 ohms. The calculate total resistance of the primary side of the ignition system with these setups exceed the recommended total resistance of the Boyer ignition. If you install 6 Volt ignition coils, which have a resistance of approximately 1.7 ohms each you get less than half the Ohm value. The total resistance in a twin is 3.4 ohms, and in a triple is 5.1 ohms. Both values are within the allowed impedance range. Only the ignition system is involved, nothing else needs to be changed. Since single cylinder bikes have one coil (3.5 ohms) they do not require a new coil. Later Norton Commandos have six-volt coils with a ballast resistor so the coils are kept and the ballast resistor removed.

The use of 6-volt coils gives a stronger spark. This transforms to easier starting and crisp throttle response. If you run a Boyer, I hope that this clears up any questions you have on the use of 12-volt and 6-volt coils.