When I pull a wheelie with my honda 250ex fuel drains out of the tube coming off the bottom of my carb. It's wasting a lot of fuel, and before I go plug it up and mess something up, what is the tube for, and will it hurt anything to plug it up?

 

The tube has three functions.
Its the drain for the float bowl. when the screw next to it is unscrewed, the fuel comes out if it.
Its the over flow. If the float needle and seat are hels open, and excess gas flows in....its gotta go somewhere, better on the ground then down the cylinder( if the motor is off).
Its the vent for the carb, if you plug it up, youll have fuel flow problems, to the float bowl.