The companies that build them bought some junk-ars expensive equipment to "flow" test them decades ago to apease the EPA.
They probably set up one carb with small airbleeds and one jet/rod combination, pissed with it till it passed testing, or passed the EPA rep a few bucks to look the other way, then started mass production.
They continue to the is day to use very small airbleeds, and extremely rich calibrations, the same set-up for just about every casting.
Problem is, they also smash the secondary fuel nozzles nearly shut, float levels all over the place, huge idle tubes, leaking bottom plugs, and about 2 dozen other problems I'm not even going into.
It is a winning lottery ticket to come up with one that works FLAWLESSLY in all areas. Most don't work well at all, some just OK, but not a single one is calibrated exactly for your application, or build by someone who knows what they are doing.....Cliff