I just went from .040 to .042 ifr's in my 1200 Dommy and that was the ticket to get the mixture screws closer to the 1 1/2 zone instead of 2 out which was still a bit lean...........

I'm not as smart as you when it comes to carbs. I run a 4150 1050AN. My IFR's are .036". IAB's are .073" and the HSAB's are .033". Main jets are 85 and secondaries are 92. My mixture screws are out about 7/8's of a turn. Almost one full turn. No holes in throttle blades. I don't see how the IFR's would affect the mixture screws. They work the transfer slots.

Ifr's feed the idle circuit and it just happened and always does..........lol Oh, and I'm not that smart trust me.......

When you use IFR do you mean the idle fuel feed restrictors or the intermediate fuel feed restrictors?
I restrict, make both smaller on my street Dominator carbs, both fuel feed channels on the primary side

Idle feed restrictors and I've found lately it's easier to tune em a bit richer especially on motors w/cam n compression..........

I've asked the questions before about if/when the ifr's and t-slots become inactive and can it be seen on the dyno or not and never got a solid TESTED answer on the t-slots but did on the ifr's. When I went to the .042's to fatten the idle/transition, my car was rich all the way to 7000 r's and the normal .002 change leaner to the high bleeds made zero difference to the wot afr's. So I went back to the .040's and .067 idle bleeds instead of the .068's and the car responded to a leaner wot mixture and is pulling like a freight train to a nice 12.8 afr reading proving the ifr's carry all the way up to max rpm's and this was also confirmed by a well known dirt track builder who sees the exact same results.............Just when I think I'm figuring some things out, I find more and more scenarios w/these carb things and the learning never stops till WE stop wanting to try and learn all we can............