The funny thing is, even when they got it is right is they ever did, it still wasn't all that good. Mileage wasn't great, and mixture across a range of operating conditions was adequate, but pretty far from ideal.
I am on a email list, "Sidedraft Central" that primarily deals with Weber sidedraft carbs, and the guy who sort of runs it is a machinist with imagination and a logging wideband O2 sensor.
He has been playing around with making his own jets, modifying them, creating shrouded versions and getting good results, increased power and mileage. Pretty interesting stuff.
He sells his parts here:
Webstore items for Member DCOE_Tuner