With the AV266 X7 combo it could be spitback if you are running with a filter and when you stop at lights etc it comes back down to the carb? With the AV264 did you try it with a x13 needle?
I am running a v3 mugello on a 30mm with a JL3 52 Pilot, AV264, X13 2nd clip and a 122 main 3.5 needle valve with a ram air. It runs slightly rich need to do a few plug chops but pulls away cleanly plug a dark brown colour (Possibly main to big).
Cheers
Stew
carb floods at low revs
Had a similar problem on a mates muggy 186 a couple of months ago,turned out to be the float height. Can't remember what manifold was on it but the carb was tilted back at a severe angle,i just bent the float up very slightly. His was ticking over fine it was only when he rode it, stopped then tried to pull away it wouldn't want to rev and would cut out.