Carter Thermoquads ~ 'More General Information'

I've been reading a lot of TQ tuning threads, and one issue I see time and again is, someone is tuning on a 1972-77 era TQ on their street/strip or race car, and they get the fuel mixture pretty good for idle, but at high rpm it goes rich. IMHO that's either too much emulsion i.e. air bleed, or the air bleed is partially blocked, or completely blocked. or the bowl vents are partially plugged. too much emulsion i.e. air bleed can do crazy things to a carb. it'll delay main metering start and pullover, but at high rpm all that emulsion air acts as a pressure jet and actually starts shooting the fuel through the nozzles into the engine, so it goes rich up top. pig rich like down to 10:1 ratio in some cases at high rpm through traps. this is where the early CS carbs, '71 340 carb shine, they have modest race oriented air bleeds/emulsion, and aren't heavy emission regulating carbs like the later ones. the 1972-74 are the next best thing. as the Federal emissions standards tightened up over the years, they met those laws by adding emulsion and leaning out the metering at idle/off idle/part throttle because that's where most of the daily street driving occurs. but take that same carb and put it on a race car or high performance engine, it can become lean as hell at the bottom end, and rich at the top end. some of the jet sizes I see put in the race car TQ's are like alcohol jet sizes, 50% bigger than what you'd expect. that tells me it's because the air bleeds in the carb top/lid are emission sized and the tuner is trying to overcome that with a bigger and bigger jet. the cure is, get an early top lid with smaller air bleeds, and less emulsion. or...another whole carb 1969-74. one thing that's often overlooked is the air bleed sizes and the richer metered top lid is the key, it contains all the air bleeds, idle jet. if you take the time to look over the design and think about it, they're all basically the same base and center plastic body- the real difference between an emission version and high performance version is the top lid. jets can be easily changed in any of them. air bleeds aren't so easy. for instance the idle circuit air/diminishing air bleeds are at an angle and plugged from the front, or inside the carb bores near venturi. very hard to change sizes without removing those plugs and doing major surgery.
which leads me to a conclusion- if you're looking for a hot rod TQ, you don't even need the whole carb. all you need is the lid. put it on any carb center section with the spec'd rods, jets, float settings, needle valves your combination likes, you're going to be damned close. the lid is in reality, the most valuable part of the entire carb, and the most difficult to reproduce if you don't have an original performance carb. all the centers sections, baseplates are basically identical.