Yes... much involved when it comes to tuning holley carburetors because each engine is different and they are set somewhat rich out of the box.
Most poeple often complain about the fuel richness smell at idle, thats where tuning on the metering block idle feed restrictions and advanced idle engine timing needs to be done to combat those issues.
As an example, my holley street avenger 770, the one that came with the car, i had the same rich smell a idle. So i had a look at my metering block and found out the IFR(idle feed restriction) was holley set .033, and that is what dictates the amount of fuel at idle before it travels to the idle mixture screws. I did get rid of the richness smell at idle by placing a small peice of .015 wire in both the IFR, effectively reducing the surface area that equals .029 size.
No matter how i adjusted the idle mixture screws for highest vacuum, i still had that richness smell. Since i was back in the game after many years getting another classic car and learning about carburetors all over again, i did many hours of research on how to tune holley carburetors, Thanks to the interwebs, theres a wealth of information to be had at your finger tips, back in the early 90s, sure you had books and magazines, but true experience was still lacking, but not for long.
Fast forward to getting a hold of a used, but clean, then rebuilt, holley street avenger 670, the crate engine model, the IFR is holley set to .026 and guess what, no more richness smell at idle, and i still had normal control of the idle mixture screws to adjust for highest vacuum. Standard holley carburetors have non adjustable orifices(IFR/PVCR/AIB-HSAB/emulsion/siphon break), unlike the race models or aftermarket units, and the only thing i made adjustable was the power valve channel restriction(PVCR), purpose to allow more fuel enrichment when the power valve opens to rely less on the main jets for better fuel economy.
I carefully drilled out the the holley set .044 PVCR to accept a 8-32 x 3/16" brass screw restrictor and used a 8-32 national course tap to create the threads, then i used a pin vise drill and drilled the blank brass screw restrictor center to .048 for more fuel enrichment through the power valve channels. I know this is a lot to take in and sounds intimidating, but there are aftermarket billet metering blocks that are adjustable, so if you plan on doing it yourself, i dont recomend using the original metering block, find yourself another holley metering blocks to practice on that are similar to the size(cfm) carburetor you want to modify, keep it matched. I went on ebay and found two clean but still usable holley 600cfm metering blocks for cheap, i planned everything out and took my time, kinda ruined one just a pinch i think, but not the other and used that one in my 670SA carburetor since the 600cfm blocks are similar. I left the IFR alone, the holley pressed in restrictors were already sized .026 and all i did was modify the PVCR to .048, and is fully functional on the ZZ4 crate ngine as we speak.
Example Video:
