To adjust the mixture screws

Get a sheet metal screw and a small drill bit.
Remove the seat. 
Remove the two bolts holding the back of the gas tank.
Remove the allen bolt holding the fuel petcock and
use a 2X4 to prop the gas tank up.
Remove the right side chrome fuel pump cover.

Locate the rear carb plug that covers the mixture screw
(refer to figure #1).
Using the small drill bit carefully drill a hole in the center
of the plug. (Do not go in too far or you will damage the screw)
The plug may come out with the drill. If not use the sheet metal
screw and screw it into the hole just enough to grab the plug.
Use the screw to pop the plug out.

Do the same to the front carb using Figure #2 to locate the plug.

After removing both plugs turn the mixture screws clockwise
to lighty seat them and turn them counter clockwise 2 and 1/2
turns.

Adjust as needed to help cold starting and correct engine idle
problems.


From Tom (Wheels):
"The correct way to do it is use a vacuum gauge. 
Hook up the gauge and turn the mixture screw counter clockwise 
till maximum vacuum is achieved, then turn the screw 1/4 turn 
clock wise. Re-hook the gauge to the other carb and do exactly 
the same, then set your idle with the idle adjustment."