Next you need to adjust your idle mixture. The adjustment screws are located at the base of the carburetor, and usually on the outside (Weber or Dellorto). Back each of them out 3-4 turns. With the engine fully warmed up and idling, slowly turn them in (do one at a time), and CAREFULLY listen to the idle quality and speed. As you turn the screw in, you will hear the cylinder misfire (it's the one you are turning in, and it's running out of fuel). Once it misses, turn the screw back out until the cylinder fires properly again. Now, turn it out 1/2-1 turn more. You are done with that cylinder. Now, do the next cylinder, then the next, until you have done all the throats.
From: aircooled.net/gnrlsite/resource/articles/dualcarb.htm