There is an idle air bypass screw that is adjusted with a screwdriver inserted into the air cleaner stud hole. It allows you to vary how much additional bypass air is let in through the four holes below where the stud screws in while allowing the throttle plate opening to remain in the proper location to keep the idle circuit active.
That's a very nice feature about some newer carbs. And I agree without an air bypass there pretty much is not another way to let more air into the eng to raise idle speed and keep the throttle blades in the proper position with the transfer slots. Holley even says in there books to drill the throttle plates for just that on their carbs with no idle air bypass. Its a simple way to let more air to the eng and not effect anything else other then raise idle speed. You cant do it through the idle air bleeds as that will effect the idle mixture. Its just a way to let extra air into the eng so you can raise the idle and not move the throttle plates. Course you know some Carter carbs like older AFB's had that big idle air speed screw in them in the front of the carb in between the idle mixture screws to raise the idle speed. Ron
