Does this bike have an ignition problem?

[Don Pearsall]

I have been rebuilding my 1979 GS1000 for a few years in order to race it at Bonneville with Nitrous. Along the way I have replaced the ignition with Dyna-S, new coils, plug wires, and many other things including rebuilding carbs. Today on the dyno, the bike was bogging and stuttering at mid RPM range and above. It freely revs to redline with no load. But with load, it bogs down. At first, I thought carb problem but now am doubting that. The plugs definitely have soot when I pulled them off after the dyno. However, when I put the timing light on it, I see the light sporadically missing and the timing marks jumping around.

That leads me to thinking an ignition problem. Any thoughts on what to check? As I said, new Dyna-S, new coils, new wires.
Thanks!

[Grimly]

What type of timing light?
I have an adjustable one, and when it's set at zero the timing appears to leap around and miss (obviously it doesn't actually, but it seems to, visually).
I find that by dialling in one degree advance the light settles down and becomes stable and accurate.
This is with the same mechanical advance the 79 and 80 GS 850 and 1000 have.

[rphillips]

Just my thinking, the ign. don''t know and don't care if under load or not, operates exactly the same in either case. The carbs operate totally different when under load.