Funny you should say that.
When I went to school, they were teaching rebuilding Q jets. The good old days.
I still have all my tools, I love them. I've got some Snap On Tools that are WWII vintage, even one that's 1937.
Anyway, in First Year Automotive Tech, we did rebuild carburetors, and tested the cars, and the one I rebuilt on my instructor's '71 Dodge Polara - his mom's car and I was his work study/teacher's pet - and when we sniffed the tailpipe on the big green Polara 4dr with 318/AT, the emissions was as low as was mandated on brand new cars, this is in 1988 and by then the max was 2% CO. The instructor's Mom's Polara was doing just over 1% CO, half of new regs, that was before the Lean Burn garbage and the first catalytic converters, mid 70's I imagine. The next you had was acid rain, because the oxides of nitrogen that comes out of the cats, besides the sulfur and other noxious gases.
I went on to be State Certified Emissions Specialist - which means your fine for cutting a cat off at home is ten times that of the average civilian, $100k instead of $10k - plus a ASE Master Technician Certification before even leaving school. There are 8 different tests/areas, no refunds for failing, I never failed one.