When I have air in my clear fuel lines*, which is fairly often when I run a two fuel tank setup, I can watch the flow of fuel, as dictated by the action of the floats. The flow of fuel is intermittent, not constant.
*Air in the fuel lines usually does not cause any problems if a slight prime is maintained. The bowls don't know the difference, and operate at ambient air pressure (plus maybe a little more for the weight of the fuel?) on the supply side anyway. It doesn't take much fuel to fill the bowls, and I expect the floats call for fuel long before the carbs would draw air from the bowls.
