Adjusting multiple IDLE speed and IDLE mixture screws on 1 engine is a great way to screw up the adjustments. Been and screwed up several good racing engine idles.

Finally the olld guys taught me several ways. AFTER the carbs had been rebuilt / regasketed correctly.
Back then we always tapped into a idle VACUUM line. My favorite way.



2, 4 , 6, and 8 idle adjustments on some engines were difficult. Add in a staggered opening of each carb butter fly and I used a piece of LOG LOG graph paper to keep track of screw turns to vacuum / to rpm changes.