Just a random one but as you 'wintered it up' did you turn the fuel switch off?
Wondering if you have "sticky bits" in the carbs as well.
If the fuel pump clicks away at the beginning okay and you know the tap is switched on, try starting it a few times then hold the front brake and bounce the front end of the bike a few times and see if you can dislodge any stuck parts by swishing fuel about.
If you suspect any moisture in the tank you'd have most likely emptied it when draining the bowls, but putting 300ml of 99% Isopropyl Alcohol will get rid of any water and bind with it then simply burn it off as fuel. Add it to a full tank of fresh fuel though.
My bike just suffered a couple of bouts of carb icing recently, first time in years, but also the first winter that i hadn't used I.P.A.
Nursed the bike back home, stuck a cupful of I.P.A. in the fuel and it ran perfectly within ten minutes, and never missed a beat all the way into work.
My bike is an alcoholic, and needs a livener to get going.