To tune a Rochester carburetor, first identify the type of carburetor it is. To tune a 4-barrel Quadrajet Rochester carburetor, first adjust the idle mixture screws and the carburetor needle, then fine-tune the air intake valves.
Begin by unscrewing the idle mixture screws on the driver's side until the RPM or Revolutions Per Minute, steadily drops. They are located in front of the carburetor. Turn the screw until the RPM rises to the maximum, then do the same on the passenger side. Remove the air cleaner, and inspect the carburetor for drips. Remove and clean the needle and float, and then place them back into the carburetor. Use pliers or a carburetor adjusting tool to put the float back in until it makes contact with the needle.
Remove the sight plug located next to the float bowl, and move the needle downwards or upwards until the fuel level can be seen in the sight hole. If the fuel level is too high, it will pour out, so drive the needle in until it makes contact with the hole.
Slowly loosen the spring tension on the air valve until it's bogged down, then adjust it until the overflow disappears. Make sure to open the air valve to a 90-degree angle and not beyond, since this can cause fuel movement issues within the carburetor tubes. That could can lead to blocked or damaged flap openings.