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 (1 1/4") long. This one came from Harbor Freight, but evidently the Chinese aren't making them cheap enough anymore and they don't stock them. Look around, or you can go to Specialty Tools Warehouse on eBay and get the 4 Piece Mini Super Stubby Screwdriver Set. Share with your friends.
Another option, and one you may already have in your toolbox: Take a normal screwdriver bit (top of picture) the kind that goes into a 1/4 drive handle. You might have one with your electric drill bits, too. Then get a 1/4" nut driver bit (bottom) and insert the bit into the open 1/4" socket end. You have an instant idle screw adjuster.