Carb Rebuilt Tuned Up and WOW!!!!

I know the feeling. What carb was it? My 69 Dart idled rough and stumbled when leaving a stop light, sometimes stalling, for years. I tried several rebuilt carbs and rebuilt myself too, w/ little change, plus many other attempts (swapped intake, valve jobs, ... ). Finally, the 4th Holley 1920 made it run excellent. No mechanic could diagnose the problem. These days it isn't hard to install a wideband O2 sensor to monitor O/F and figure such things out.