Well your old Holley has them too, they are pressed in brass that are not replaceable without taking a tap to the main body. Not something to mess with in either case unless you have a clear understanding of what the change will do to the fuel curve. The outer air bleeds are idle air bleeds, they along with the idle jet in the metering block control the idle and transition circuit fuel, as well as the duration of the transition circuit. Since the idle circuit needs less fuel than the transition circuit, you have a mixture screw to adjust that with. The inner air bleeds are for the main circuit, they along with the emulsion bleeds in the metering block control the starting point of the main circuit, how aggressive it starts, and the fuel curve of the main circuit.