There is no secondary idle circuit on a Holley 80457. This is a 4160 model Holley, which have a secondary metering PLATE, in place of the model 4150's secondary metering BLOCK. ( this is the main difference between the two models, most other parts of these are interchangeable). As for your hiden stop screw, it's either there or not, it's not hidden, if it's there, it's on the passenger side of the carb, where the throttle rod pokes out. I've never had to mess with this screw,( all my engines idled without needing to have extra air flow) and never really paid much attention to what carbs had it and which ones didn't. The only Holleys that have a secondary idle circuit, are the 4150's ( some not all) and these are obvious, as they have the mixture screws sticking out the sides of the metering blocks ( not plates)
I'm beginning to think the thing has some other issues. like it's pulling gas from somewhere other than the idle circut. It's got the adjustable air bleeds in the center section of the carb, might those have anything to do with it running rich at idle? Sorry guys I know that I've about beat this one to death.... but seems like everyone has learned a thing or two.
, you can call it whatever you like. Opening the secondary air gap simply provides additional air for idle speed, so that the primary can be closed down a bit. This is useful when setting the idle with only the primary causes the transfer slots to be uncovered. This serves the same purpose as holes drilled in the throttle plate(s) (which is the next step). Some Holley’s are notorious for needing this with radical cams (3310's for example) Some Holley’s have holes in the throttle plates from the factory thus work without this on radical cams. Demon now has the "idle eze" feature to overcome this problem. 
