I replaced the original, now badly cracked coils on my 1979 A1 last year. I too was very confused initially about the resistance requirement and whether or not a ballast resistor was still required and with what specification of coil. I know from my experience in running old cars in the late 70’s that ballast resistors were used to enable cold start – when you engage the starter motor, the battery voltage drops and you get a weak spark. With a ballast resistor in series with the coil, it was very simple to bypass the ballast resistor every time the starter motor was switched on – hence better spark when starting.
My understanding, after a good deal of reading, is that our main issue is the Igniter unit designed by Kawasaki. This is effectively the simplest form of electronic ignition unit in that it is simply an electronic switch that replaces a conventional mechanical contact breaker or “points”. This electronic switch uses a “Darlington” transistor which is simply two transistors in a servo configuration which means that one transistor (imagine it as an electronic switch) is used to switch another transistor. This is like using a small switch to operate a bigger switch. This configuration enables the “switch” to handle more current and in turn to produce a higher voltage spark. Worth remembering that we get a spark when we turn the switch off and not on! It’s all about rate of change of current and it’s easier to get a very fast switch off than switch on.
Another approach to electronic ignition is the CDI or Capacitive Discharge Ignition. I won’t bore you with the details but this works completely differently to our units in that it charges up a capacitor to 300-400 volts via a transformer and then switches that charge through the coil to create a spark. If you want more info on the different systems, see
what-when-how.com/automobile/electronic-ignition-automobile/
The issue we have with the Kawasaki 1300 igniter is that these Darlington transistors have a maximum current rating. If we try and flow too many amps through them, they will burn out. Kawasaki have not published the details for these transistors so we don’t know what their current limit is but, from what I understand, is likely to be around 5-6 amps. With the stock coils and ballast resistor, the ignitor will see about 4.5 amps (assuming a 14 Volt supply when engine running) which is within the transistor current limit. If we were to fit 2.2 ohm coils and no ballast resistor, the current flowing through the transistors would be about 6.5 amps which could end up overheating and damaging the transistors. As with all electronic components, exact specifications will vary and they will be given a “tolerance” value, so in some cases, maybe you can fit 2.2 ohm coils and run without any major issues. However, the Kawasaki manual states a minimum resistance for the combined coil and ballast resistor of 2.7 ohms – which is 5.2 amps at 14 volts. Most of us are therefore hesitant to go much above this figure. I fitted 2.2 ohm coils with 0.4 ohm ballast resistors which will drive 5.4 amps through my igniter and so far, this has worked great.
For more info on my experience and some pictures, see
www.kz1300.com/index.php/forum/electrica...1300-how-to?start=78 and page 14.
For interest, my calculations for various options detailed below:
And a pic of my installed ballast resistors (after removal of the stock mounting brackets):
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