Modern EPA compliant fuels just don't store well.  Stihl recommends in their owners manual that you remove the fuel from their equipment if you are going to be storing the equipment for more than 2 months.  A fuel test I did showed that the fuel I bought at a local gas station started to decompose in just 50 days.

When you decide to put your bike in storage - if you leave the fuel in the tank you need to add a fuel stabilizer like Sta-Bil and run the bike long enough to get it in the petcock and fuel lines - then after you shut the bike off, I would recommend you open the screw on the bottom of the carb and drain it (if your bike has this screw).  If you bike doesn't have the screw - disconnect the fuel line and plug it...then run the engine until the fuel in the float bowls runs out and the bike stops.