Carbs or something else, maybe?

[Sannox]

Checked all the carb inlet rubbers when I had the carbs off, all nice and clean and in good nick, no splits, the whole airbox is as new, a friend suggested kinked breather pipes but I know the issue isn't there, as the carbs are now spotless, inside and out, I'm ruling them out for now, though they do need a balance after my tinkering, I wonder if just a carb balance would sort the issue out, will see. I am wondering about plug caps, got to fire it up in the dark to check for arcing, the plugs are fine, 2k miles old but could be worth a check anyway, the battery is new and charges just fine. Will keep at it :-)