Just put a set of high lift 262 duration cams in my 2.0L zetec. The engine runs on a set of honda blackbird carbs. Needness to say the cams messed up the fueling, so I set to work with a wideband meter to put it right. (note idle screw is an air screw not fuel)

results - idle mixture (car at operating temp after 20 min hard run)

170 main, 42 pilot with 1 turn out of idle screw: idle = 11.76 AFR

170 main, 42 pilot with 3.5 turns out of idle screw: idle = 11.32 AFR

170 main, 40 pilot with 0 turns out of idle screw: idle = 18.15 AFR

170 main, 40 pilot with 0.75 turns out of idle screw: idle = 16.61 AFR

160 main, 42 pilot with 0.75 turns out of idle screw: idle = 12.19 AFR

It's not really making much sense. The carbs have just had a good cleaning. Nothing else has been changed. How can there be such a vast difference between a 42 and a 40 jet. Logic says that a 42 jet with 3.0 turns out should give the same AFR as a 40 1.5 turns out. Or am I missing something completely ?

Just a guess, but if you are having to alter the idle speed as well, that will be having an effect on the overall fuelling the engine sees as it will be trying to pull fuel from the main circuit...