Nissan 30a3 mid-range misfire

My 30a3 motor runs fine at idle and up to about 2000 rpm under load, and runs fine up to high RPM with 'just' the throttle, then as I slowing open the throttle in gear, it starts to miss slightly and stumbles more, the more I open it up, and won't wind up, misses badly, and has a loud low bogging sound. I have cleaned the carb in an Ulstrasonic cleaner, checked the fuel pump, filter and lines. At full throttle under way I have tried applying some choke and it doesn't help, nor does squeezing the bulb.
Are there ignition issue the would only present themselves under a heavy load?

Thanks for your help

Ron in Port Orchard, WA

What do the plugs look like? Have you tested the ignition system? Is the carb and ignition in sync?

Plugs are running a bit lean, but not too bad, I don't have the test procedure or specs on the ignition system yet. Will these ignition systems sometimes work well OK at no load, and present a problem under a load?

If the ignition is marginal, it might stumble under load. Odds are it's still a carb issue, though.

Ohm tests for the trigger and exciter coils are within specs, but when measuring resistance between the brown lead wire and the high tension spark plug wires, one plug wire is within spec at 2500 ohms, and the other is way over that, sometimes reading open......perhaps a cd unit?

Hmm. Brown is the ignition kill wire to the stop switch, right? You might have a marginal CD box...