Frequently asked question!
Apart from Tri-Spark Triple kits which use three 12 volt coils, all twins and Boyer triple kits use two or three 6 volt coils. Actually some guys prefer 4 volt coils for triples with electric start.
Basically, the ignition systems need primary total resistance of the coils to be between 3 and 7 ohms. The lower the resistance the brighter the spark. If below 3 ohms too much current will flow and damage the transistor box and if over 7 ohms the spark will be weak or non-existent.
Commandos from 1971 and T160 Triumphs have 6 volt coils as stock. A ballast resistor (which must be removed if fitting electronic ignition) reduces voltage to the coils to 6 volts.
Various 2 lead coils are available. The one we have had the best success with is the Dyna 5 ohm type. 2 lead coils (most especially Boyer brand) generally need to be heat sinked and kept in a good air flow.
Which way around to wire the low tension leads? It doesn’t make much difference – on a positive ground bike if you wire the positive terminal to ground the spark will jump from the plug’s central electrode outwards – wire it negative ground and it will jump the other way. With 2 lead coils one spark will jump one way and one the other.
Best coils – the consensus seems to be that the expensive German PVL type are the best and we have never ever had a warranty claim on one having sold thousands over the last 30 years. The new “genuine” Lucas type seem to be good and a lot have been sold with only one claimed problem – as yet to be returned and tested. Tri-Spark also offer their own coils which seem to be very good.
Rare and much sought after part fits most twins (including N15CS) and singles (apart from G80CS) 1963 onwards. We have just had 100 made – order by part no 04-8300 $116.90 Canadian.
