It’s driving me mental.

Some of the symptoms are contradictory. It seems to be perfect on the first run through the rev range. It always revs cleanly in neutral (before and after the race). Coming onto the straight (after heavy braking) it always runs badly initially (tried coming on between 5000 and 9000 rpm)
It would run badly regardless of the revs (maybe one cylinder?) then come good for a bit.

I’d almost convinced myself that it might have been related to the “G” involved with the braking.
The “intermittent” nature is making diagnoses difficult. (Too difficult for me.)

It can’t be fuel delivery (blocked breather etc) because it comes good and revs cleanly to redline.
For the same reason it can’t be anything “permanent” like jetting.

I can leave the fuel on all day, and it starts first kick, so the float needles are working. (At least basically.) Do these carbs have an “overflow”?

I’ve tried 2 sets of new plugs.

Suggestions?