You don't replace a carb for high idle, that just indicates not smart enough to adjust it out or fix it. No insult intended of course. Several ways of getting that back down.......... .vacuum leak is an obvious one. You should be able to choke carb out to completely kill engine by dropping idle set screw more and more, not having it means something MAYBE wrong with carb but 95% of them are fixable. You have to play the idle mixture screws and idle speed screw against each other.

Hoping you still have original carb on it. Only way they can high idle to not be fixed is throttle shaft leaks from wear and even that can usually be fixed. Of course corrosion from ethanol can cause issues now.

At our shop back in the old days we were known for never buying new carb to fix and customers loved not getting plugged with the huge bills of doing so. In our view the original carb was the one best metered to your motor if stock, any over the counter ones are condensed from the 200-300 different ones used to maybe 50 (don't be surprised if only 25 now!)  part numbers overall and you get shortchanged there for sure. All the while they are telling you how much better the new carb will perform. Ain't no way. Some are close but others are terribly far off, and why we quit pushing new ones back in the day. It got much worse as emissions carbs got so customized to each vehicle and motor. I saw so-called 'absolutely correct carb by number and application' not run at all and then rebuild old one and runs perfect more than once.

Although I've done it no need to cut filter either, the first OC will show you, look at the oil in strong light and you can generally see the 'glitter' in there to make the oil look like liquid gold. Let the oil settle and then pout it off to see what remains. Depending on engine if race or stock, oil changed after 30 minutes running or up to 250 miles. Make the next one after that a little sooner than your norm then go to the norm.

If not driving 20 miles you can drive with open header but any issues past that will be with the police.

What makes you think you need to replace the carb??, it was working good before the re build, right?, might want to go back re check everything, cam/ignition timing, vacuum leak and what ever else you have, lack of power and high idle don't mean the carb is bad, probably just need some tuning.

'it would always choke out when I cut it off.'

Never heard a description like that in 40 years, what are you trying to say there? ALL motors 'choke out' when you turn them off.

'If I turn the throttle adjust screw out though, nothing changes.'

Not rocket science, bend over and see if the screw is out in space and not touching linkage, obvious that will do nothing but you must make the effort to look. Car won't fix itself.

'if I pull up on the throttle, it idles at a reasonable speed until I let go.'

That has all the earmarks of a not strong enough throttle return spring and a very dangerous condition, don't fix it later, fix it NOW.

You should be able to lower speed with screw to where engine dies or carb not right. Linkage, cable issue, dragging may all be a problem. You always treat not returning to 100% dead idle as a safety issue, enough people have been killed by it in one way or another.

MTX or ATX? Idle should be around 700-900. Lower is better if smooth.

I mean choke out as in it would sit there and try to keep running but coughs basically and finally die. It doesn't Do that since I rebuilt the motor though. And okay. I'll check the spring when I get home. And also, it never idle down. It just stays at around 1500 even when it's warm.

As he says. You mean 'dieseling' or 'afterrunning', often an indicator the throttle at idle is too far open and you describe that in other ways. You need to do what it takes to get the throttle back on true zero, it is sticking or something holding it slightly open and the cause of your issues.

Poor gas leads to that as well, and why in the mid '70s all these cars started getting the electrical solenoids on the idle. The normal throttle setting to get even 600 was enough to cause afterrun and the solenoid drops lower than normal idle to truly close the throttle and stop it. Why there are TWO settings when you have a solenoid, idle and all the way off. You check them both. Of course does not matter if enough friction in cable or linkage to override the throttle spring to let throttle stick. Sounds like you are there, the statement about being able to force linkage to zero and then speed lowers says so.

Look enough times and you will even see the engine diesel to crank back up and RUN BACKWARDS, seen it plenty of times, the crank is turning the wrong direction..... .......

As could a bad decel valve if you have one on there and it failed in the necessary way to make high idle.

The being able to lower speed by simply pulling back on linkage says issue there though. Make sure the pressfit where linkage sideplate joins the throttle shaft end is tight, if loose you can often peen the area with a slightly rounded small tip punch to tighten it back up.

You misconstrue, go back and read again.. No one said to change all the parts, only which ones could possibly be an issue.......if one uses brain and checks parts for good/bad first instead of just throwing new parts at it then often maybe buy one part only. I've done it so many times I cannot count.

I sold and installed many rebuilt carbs and I reiterate this simple fact. No way will you ever get a new rebuilt carb that matches your engine better than the factory one that was on it to begin with. Absolutely no way. It was even like that to a certain extent back in the '70s when there were so many more carbs available to pick from then and much much worse now with reduced inventory. Some people back then as well simply did not understand that and insisted on the new carb anyway. Many came back complaining later of how car did not run quite as well with new carb or get as good gas mileage. Take the old one and rebuild it and back on car and better almost all the time. People just have it ingrained in their DNA that new is better and absolutely not necessarily true at all.

I am so much cheaper than you can imagine. I generally often rebuild carbs using no tune up or parts kits at all (maybe making one main body and/or throttle body gasket myself) and they almost 100% always run perfectly afterwards. Piece of mind by buying new carb is for those who do not understand them, I've never replaced one on my personal vehicles in my entire life and often tear them down to fix one exact part since I know pretty much what's wrong with it before doing so. Often I can repair and reuse the same part.......... ....

Same thing with modern PCM controlled cars, I fix all my own issues and extremely rare to not get it right the first time. I've never paid to have any car of mine fixed by someone else over a period of some 40 years+ now. THAT'S cheap......... ...

 I know they stopped using decel valves after a certain year, mines a 78 and it never had one. I forgot what year they stopped in its in my chiltons though.

 One thing I do, if my carb is under suspicion, is turn in the mixture screw far enough to see if it will slow down and kill the motor.

 After I had my motor rebuilt in 1988, I had a prolem I think maybe it was too fast idle. When I found I couldnt affect the motor with the mixture screw I called the guy who rebuilt it, and he said` too much gas getting through the top half`. I had no idea what he meant back then. But I found out the power valve diaphragm had ruptured or tore, and the vacuum signal wasnt holding the power valve up so it was providing enrichment at all times rather than just under load )low vacuum). After I replaced it the engine idled a lot better and of course it got better mileage. Maybe wasnt quite as fast.
 But thats an easy test, turn in the mixture screw to see if it will idle down and cut out. Later use a vacuum gauge to get the mixture close.

 There was already some long debate here in another thread on the decel valve thing. It gets confusing.