Hi fellow enthusiasts.
I hope someone might have some knowledge on these symptoms which they would be willing to share. All suggestions appreciated.

My 1989 NSR 250. Racebike. Seems to be a cross between MC18, and MC18II. (PGM II)

I’ve spent a lot of time solving a lot of little issues and generally getting the bike up to standard.

First ride yesterday (If you don’t count a few runs up the “test track” - My street!)

The good news. I love the feel of the bike, handling is great, brakes are good. (I prefer it compared to my “sorted” Ohlins Equipped Ninja 300 SS300 race bike.

Motor feels “occasionally” “sweet”, but there lies my problem.

The bike starts first kick, idles nicely, and once warmed up, revs cleanly. (Probably revs cleanly cold as well - but I love engines.)

It might be coincidental, but it seems to run nicely through the range just once, then “hesitates” after the gear change. From then on there is frequent random hesitation/missing/rough running.
This seems to occur at random revs, and intermittently (but its affecting the engine most of the time). The bike will run up to redline even with the intermittent rough running. I stayed out and rode 10? Laps. It doesn’t get better or worse.

Background:
I’ve disassembled and cleaned the carbs.
Airbox. No filter.
I’ve tested the coils. (When cold)
New plugs and good looking caps.
Confirmed the exhaust valves test correctly.
The plugs “Read” well.
The bike seems to run around 70 deg.
The fuel is fresh BP “98” at 40:1 Motul 800 (full synthetic) - Is this a bit “lean on this type of bike? This would be pleanty of oil in a 125cc MX bike, but I’m new to pre mix road racers.

The bike feels very well tuned and pulls well at all RPM except for the issues described which seem to randomly occur between about 5k and redline. This leads me to think its not anything like crank seals. Something intermittent, probably electrical.

The wiring harness is as you would expect on a 30yo modified race bike.

I’m running out of ideas and need help from someone with more experience. I want to race the bike next weekend. (“Big Chill” historic meeting, Stanthorpe QLD)

Thanks for reading.