Found this:
https://www.xs11.com/forum/showthread.php?t=34875 along with this comment a ways down:
I'll repeat this... if converting to later stick or mini coils, even if the coils measure the same ohms, you have to verify if they are designed to operate on a 'dwell control' type ignition. If they are (and almost all coil-on-plug ignitions now feature this) and your ignition doesn't have this, the coils will burn up...
What happens is the dwell control ignitions limits the duration of the 'power pulse' (that fires the plug) to a maximum time (usually less than 30 ms). At high rpms, it's not needed as the firing pulses are short. But at low/mid rpms without the dwell control, the pulses will be longer and the coil will have time to saturate. Once it reaches saturation, current will go up quickly and the coil will start heating. Because of their compact size and lighter-gauge wire, these coils can't take this for long.
I found this out when looking for new coils for one of my XSs; Dyna makes a 'mini-coil' (same ohms, same mounting, more compact) that points the plug wires straight back just like the OEM coils, so it looked like a perfect solution. But I was informed by their tech that without this dwell control built-in to the ignition, they would fail quickly.
So my question is: Does the Dyna S or Dyna III have a built in dwell control function? If not, it sounds like these could go up in smoke a little early, according to this writer.
Further down the page he writes: The big advantage to a coil-on-plug ignition is they can 'tune' the coil for a much better spark at high rpm without having to worry about saturation at low speeds. A conventional 'multi-plug' coil, because it has to fire more often, has more trouble producing a big spark. But to avoid a large, bulky coil that would be needed to operate at all rpm ranges, they use dwell control to limit the time the coil is energized to the same amount as when running at high rpm.
The XS ignition system isn't all that bad; you're only firing two plugs, unlike the older cars where a single coil would be firing all the plugs. Many of the newer cars also use the 'wasted spark' system, with one coil per pair of cylinders. But dwell control would be a nice upgrade, then you could use a better coil. I'm sure you could get at least close to the performance of a coil-on-plug system if that were available for these bikes...
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