You haven't stated (I haven't seen) what mods you have done to the motor or what calibrations are in your carbs.
Crusing could be at 20 MPH and if you were on a flat piece of road with a light engine load you'd be on your pilot circuit. If your crusing at 80 MPH you might be fully on your mains if climbing a steep grade. Very nebulous term cruising is.
However
I'll assume that you are talking about a 50-60 MPH cruise and that accelerating from there with WOT in 4 gear you feel a flat spot???
If so your needles may need to be lowered and your main jets may need to shrink, depends on what the plugs look like; you could be on the other side and in a lean state which would require a higher needles and larger main jets.
Do this: Get the motor to proper operating temp, cruise the bike as you did for 30-45 seconds with steady throttle input, pull in the clutch and kill the engine roll to a stop. Now pull the spark plugs and have a look. If they are black your needle is too high, if they are white your needle is too low, if they are coffee brown you are good. If you are significantly below 3/4 throttle while doing this the slide cut away needs to be increased/decreased. The needle exerts its influence between 1/2 to 3/4 throttle, the cut away from below 1/2 to about 3/4.
Fix any issues and repeat until your achieve coffee brown, keep in mind that Amals and Nortons are mutually self destructive. If your carbs are old the slides may be leaking air, screwing up the mixture.
Regardless of the slide condition you can tune for WOT, cause the slides are out of the equation, you just need a larger, longer road.
Same drill but holding the throttle wide open for 30-45 seconds may be difficult, a dyno with a sniffer will be much safer. Anyway jet untill you have solid very obvious, distinct brown on the plugs.
Here is tip that has helped me a lot when tuning carbs. I put masking tape on the twist grip body and put white-out on the grip, I then mark out 1/4,/1/2, 3/4 and full trottle positions. When I ride and start having a problem I can see what position is giving me grief and determine quickly if my issue is with the pilolt circuit, the cut-away, the needle or the main jet.
