@6v6gt
Tis indeed a 90 degree V twin stroker.
I do actually know the firing pattern intimately as I mapped the ignition on this many moons ago using my mechanical simulator, which is basically a plastic copy of the flywheel with steel lobes (bolts inserted and filed to the correct size/width) and spun by a radiator fan motor and mounted in a box. Two VR sensors are then screwed in place on the box and the signal from these VR sensors plugs into the wire harness on the bike. The top face of the box has a degree wheel printed on it so I can then read the ignition timing with a strobe, just like you would on a normal running engine. The biggest issue is the fact that it has a disk spinning up to 12,000rpm and is a touch dangerous 
I'm using the NSR250 as the base of this project mainly because I know them inside and out having raced then back in the day, and worked on them since the mid 90's.
To explain the purpose of it all. Every now and again I need to check the operation of a CDI unit. So rather than pull one of my bikes to pieces and then fill the place with 2 stroke smoke and noise, I can just take the CDI to my bench, plug it into the loose wire harness and then plug in to VR sensor input to my ignition simulator. From here I can check that the plugs actually fire, the exhaust valve servo is operating correctly and that the rev counter works. There's quite a few other little bits and bobs such as air solenoids that are RPM and throttle position dependent and I can check all that.
So as it is now, if I plug my electronic simulator into the harness, everything works as it should. But the one issue is that I can't see the ignition advance, which I could with the mechanical system by using a timing light.
That's where my capacitive clamp mini circuit comes in. If/when I integrate that into the simulator then I should be able to measure the time difference between the VR pulse and the spark plug pulse and get a pretty good idea of the ignition advance. At least that's the plan. I have two working circuits. One uses a thyristor and the other a transistor. Both use a 55 5 ic to output the 5V square wave that the Arduino can read.
The parallel project (which sort of ties into this) is to make a DC CDI unit.
I made another little circuit (555 ic again) that takes the VR signal and converts it to a 5V square wave. From here I should be able to put that into my DIY CDI and then do what I need to do with it through code on an Arduino.
The DC CDI has been a bit of a pain so far. Make a 12v to 300V DC to DC converter is definitely pushing my capabilities, so in the interests of actually sparking a plug I cheated and used a cheapo 12V to 400V module (set at 300V). It uses a UC3843 ic to control the PWM, so I tapped into pin1 (compensation) and by grounding this one can turn off the PWM output.
Also removed the output capacitor so that I got a 300V pulse rather than filling up the cap with a steady 300V.
The output is then connected to a 400V 1.5uF cap, and a couple of UF5408 diodes. This is switched to ground through a BT151-500 thyristor, and dumps the goodness into an NSR250 coil.
The timing for the UC3843 switching and SCR switching is done by an Arduino Uno right now, at a fixed "nonsense" frequency (approx. 16Hz or what would be 1000rpm), just by switching a couple of pins on and off. Seems to work albeit not particularly powerful yet, but I'm hoping that's more down to the timing of it rather than the components in the circuit.
Anyway, Just finished work so I'll have another play, and await the dreaded call from the wife wanting to know why I spend my life at the factory and not at home.....
Cheers for now, and sorry for another long post.
Matt