First off - had you drained the fuel bowls? I Know you said you drained all the gas - but if you didn't let them drain (AND evaporate), it is possible that they got all cruddy.
Did you run the petcock on "PRI" for a while before you started trying to start it? If not, that can cause you to inadvertently flood the plugs (because you'll be starting, grabbing throttle for a long while before the bowls fill, and they won't fill at the same rate since the #1 carb is closer to the fuel source).
Another thing I might suggest is that you use the kick-start. I've learned on a few of these bikes that they don't have the best electric start (especially when cold).
Come to the bike after it has rested for hours. Turn petcock to PRI for a few minutes (just incase the bowls aren't completely topped up). Then turn it back to "on". Now pull the choke to the half choke position. Put your hand on the throttle but DO NOT apply any, just have it ready incase the bike fires up. Give the bike a nice solid kick. If nothing, try one or two more kicks, still WITHOUT throttle.
If you don't hear as much as a pop or two, then switch the choke to full choke. Now give it a few solid kicks. If you aren't getting popping at this point, then perhaps your carbs will need to be cleaned.