Your carburetor is the heart of your car, this video from Luke Finley (ThunderHead289 on YouTube) explains how to properly adjust idle mix screws on your carb using a vacuum gauge with a hands on demonstration.
1. Make sure engine is fully up to operating temperature.
2. Find source of full manifold vacuum (most will use full manifold port for vacuum advance.)
3. Turn mix screws all the way in until they are seated then back out to 2 1/8- 2 1/4 turn
4. Leave air cleaner on before cranking.
5. Turn adjustment screws evenly until you get the highest vacuum read possible first.
6. Adjust carb evenly until manifold vacuum reaches its highest point