I have the Dellorto book, but it's not mentioned until far later when trouble shooting (which I find strange) To be fair, I'm going to balance via a manometer (I'll document, for fun) which seems to be a rare approach, but the best! So I want to understand the best approach to set mixture adjustment at idle, I have conflicting approaches (I'm favouring the latter). I'm guessing the aim of the game is to get the best vacuum / high idle, but, honestly, so much searching has not clarified matters for me. Approach 1 Adjust the Idle Mixture screws to produce the strongest manifold vacuum for each individual barrel (strongest vacuum, or loudest hiss, or peak rpm). Don't worry about balance, just make each one as strong as it can be. On properly jetted Dellortos, the idle mixture screws usually end up being out 3 to 3 1/2 turns from fully seated. Anything more than 4 turns gets beyond the effective taper on the needle and will make no additional change. Anything beyond 3 3/4 turns probably means larger idle jets would be better. Anything less than 2 turns probably means a smaller idle jet would be better. Some older Webers used a pretty coarse Idle Mixture screw, and the final setting could be as low as ¾ to 1 ½ turn. The peak vacuum/ rpm will probably hold over a range of screw movement, so adjust the screw each way… in and out… until the vacuum/ rpm drops noticeably from the peak. Note the screw positions where the drop-off occurs relative to the peak. After the range is established, the final setting is made by backing the screw out a bit, then turning it in and stopping half way between the high and low limits you just found. Approach 2 The idle mixture 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. Play with it, and adjust to achieve maximum idle speed. The biggest mistake in this part of the adjustment process is not waiting 10-15 seconds after an adjustment of 1/4 turn at a time, for things to “stabilize”. Don’t rush it! At idle it takes a bit for fuel to get flowing, or stop/evaporate, don’t be in a hurry. When you find maximum idle speed for that cylinder, I go 1/2 turn richer with Dellortos, and 1/4 turn richer with Webers. This will result in a more stable idle speed as temps and conditions change.