Ordinarily, I'd largely agree with this statement, but you have to ensure your core parts are within serviceable limits, or you run into issues like this poster:
In a nutshell, he chased a crappy idle problem down to worn throttle shaft bushings after rebuilding a believed good carb.
I'm not trying to dissuade you from using a used carb, just be damn sure whatever used one you buy is usable and only needs basic organic repair to properly function...then and only then can you begin truly tuning your carb for effect. Happy hunting and I can't wait to see some good reports on this one!
