The metering screws do control the idle mixture but their settings also affect the transition circuit too.
The main jets are in the main metering circuit which help control the A/F when the main circuit is working.
You have a few circuits to deal with, idle then the transition and then the main metering circuit, then the secondary or WOT. All need to be tuned to the correct A/F range, and depending on the carb, they have replaceable jets for each circuit for tuning.