The question being: how to make an ECU controlled CDI system?
I'm getting a lot of inspiration from this article: A high-energy capacitor discharge ignition system [alt] by John Clarke (Silicon Chip September 1997). There's now a Dick Smith kit for this, I think! K3307.
Here's a page on Transalp CDIs, including a schematic. The Transalp ones include their own high-voltage generators. And some notes on a PIC-based programmable CDI
This could also be used to power the XLV's stock CDIs, and this is probably where I'll start.
So, I'm putting together a new version of the circuit to get around this, and rerouting the 'kill switch' lead to turn the inverter off rather than shorting it out. Additionally, the 1uF output capacitor will get a lot smaller and the regulator circuit will change to compensate for that, and a 555 circuit will be used to switch the inverter on and off with a duty cycle of ~95% at ~1kHz, imitating the voltage characteristics of the coil generator. An extra diode or two need to be added as well ...
Well, that didn't work at all. I could make it run by dropping the switching frequency to a couple of hundred hertz, but the voltage output was disappointing. I also tried gating the voltage on and off with a pair of transistors, but that did the same thing ... locked up and strangled itself, and another MTP3055V hit the bin.
As a really dumb test, I tried wiring a mains transformer backwards to feed the CDIs, but with a couple of rectifiers to knock out the negative-going sides ... which idled very nicely, but wouldn't rev above 3000rpm. I've got this horrible feeling that some part of the advance circuit depends on the generator input frequency: either that or the transformer just isn't producing enough something.