Bike not starting or running

After having opened up the engine and checking timings etc, we started the bike again and it sounded like it wasn’t getting enough fuel. We adjusted the floats, there now at about 9mm and the bike sounds like it’s getting fuel. However it won’t start unless we block the air by putting a hand over the rear carb (Airbox or tank isn’t on currently) and then we can’t get the bike to start or idle without giving it choke. The rear cylinder seems to be mis-firing despite us having checked the timings and having checked the spark and seen it. We’ve used carb cleaner and re-built them, checked the size of the jets, checked in the engine.

Not sure what to do. New carb floats are on the way. Any help appreciated.