Yep, it's a tough problem, and I don't have a perfect solution for it. Short of removing the engine and removing the back cover, I couldn't think of a spot to use a timing light either. The best alternate I found is to pick up signals from the stock VR sensors, feed it into the following circuit to generate a smoothed signal (a slight modification of the previous inductive pickup circuit), and match the Microsquirt output to the VR signals.jigglypuff, I am finally getting back into my efi conversion. Have you figured out how to verify base timing? I dont know what to shoot a timing light at, espeicially in your case since you aren't using the stock vr sensors.
Also I have a copy of the stock timing map if you need some info on that. I will go out and console into my Ignitech and pull the curve if you want to start with that for you base timing.
I was going to just use my ignitech for timing, but I decided against it, since it can only reference TPS and RPM. It cannot adjust for load.
I'm assuming the stock VR sensors are advanced 15° at crank/idle, and the Microsquirt is fixed at 15° during the timing process. I'm recycling this image from a previous post: here's a sample of what the "matched" timing signal should look like:
As opposed to the inductive pickup method, there are no green/blue overlaps. The signals are much cleaner and less prone to induced noise.
It's by no means perfect, but the bike is running pretty well so far from idle to ~3000 rpm. There's a noise issue in the hall sensor that's been plaguing tuning for the past week (among other things, though) and has kept me from revving higher.
If you're willing to share your base timing numbers, that would be marvelous. I'm currently using MS2/Extra base numbers, which look fairly safe to me.