Think of it as a tiny toilet bowl . when you flush (open the throttle) the float allows more water (fuel) in to replace whats been used. The purpose of the float mechanism is to keep the toilet from overflow (flooding)It only lets in whats needed as its used up. The toilet is remarkably similar to the carb except that the carb is variable speed and the toilet is all at once. This could be under the heading of "strange but true"