I've had it happen on a snowmobile before, but it is either bitterly cold or in deep snow, or both

 

Well I had 3 cars that were freezing their throttle plates, you start loosing power, then you close the throttle and it won't close, then checking inside befor it melts showed the carb throat to be 1/3 of it's original size. I turned the engine over not to hydrolock and stopped it right away for 5 mins and was good for another 30 miles, it took a lot of gas. Then I fixed the hot air intake of the car. On the VTR the slides may stick and the mix will be off and will probably die. This happens because of the gasoline chilling effect, when it evaporate it removes some heat (put gas on your hand and it feels cold) and freezes the air witch can no longer hold it's moisture that is deposited on the surrounding surfaces forming some ice.

 

Too cold to freeze the carbs on a snowmobile. More likely on a cool foggy day. When it is cold enough to freeze than all the humidity in the air gets frozen out and the air is very dry. But on a foggy day, the increase in velocity of the air getting pulled into the carb along with the vacuum created by the intake stroke can cool the air or the carbs enough to cause ice to build up on the carbs. Here is an article about it for airplane carbs, but the same applies to motorcycles, but not quite as common: http://en.wikipedia.org/wiki/Carburetor_heat