I wasn't gunna post anything but since you dont have any replies or many views ill put in my 2 cents. With my bike I use to have problems when it was cold, Id get some air in the lines. If you have a choke try setting it 3 or 4 times before attempting to start. Also if its a vacume system turn on ignition so you can hear the vacume pull, then click it off then on, and off, and on. Just wait each time until you hear the vacume stop before turning it off this should get any air outta the lines as well. If you have a reserve switch make sure its off. Also make sure you refilled the tank
Most have a vacuum operated petcock. That means no fuel will flow until the engine's cranking. Because the bowls were run dry, it will need to crank on the starter to create a vacuum, which opens the petcock, which will then start to allow the carb bowls to refill. Meaning keep cranking. It will take a good thirty seconds or so. Maybe you've already figured this out by now.