How do I adjust the idle mixture?

Pull the carbs and remove the idle mixture screw caps. Once the screws are exposed, turn them all the way in (gently - not too tight!) then back them out 2 1/2 turns each. This is the basic setting. It can be further modified after you put the carbs back on the bike. (With a Muzzy/pod filters setup the screws will be opened a little more.)

So, put the carbs back on the bike; go for a ride. Come home with a warm engine. Park and leave it idling. Put on a jersey glove or something to protect your hand from the heat. Use a small screwdriver to turn in each screw until the cylinder for the screw being adjusted starts to miss, then turn it back out 1/4 to 1/2 turn.

Alternate method: Set the screws out to 2 turns, then back them out 1/4 turn at a time while blipping the throttle. If it hangs at all, it's too lean. Turn the screw out, which richens the mixture. If it drops below idle when returning, it's too rich. Turn the screw in, which leans out the mixture.

For either of these methods to work, valves must be in adjustment and carbs reasonably synced. You can sync them visually before putting them back in.

Note: If you can get your mixture screws within 1/4 turn (90 degrees) of the proper setting, it's usually close enough to get the engine running smoothly.

Note 2: Turning the screws IN decreases the amount of gas at idle (leans it out). Turning the screws OUT increases the amount of gas at idle (richens it).

Note 3: There isn't much room under the carbs for a screwdriver. Finding a short screwdriver and making it even shorter by cutting off part of the handle will usually work. Then there's Super Stubby:

Yes, it's all of 33mm long. It's available at Harbor Freight for the low, low price of 2 for 99 cents.

Another option, and one you may already have in your toolbox: Take a normal screwdriver bit, the kind that goes into the tip of a 1/4 drive handle. You might have one with your electric drill bits, too. Then you get a 1/4" nut driver bit that goes into the same screwdriver handle. Insert the flat head screwdriver tip into the open 1/4" socket end of the other bit and you have an instant idle screw adjuster.