the whole procedure for carb adj is here
www.vw-resource.com/34pict3.html#carbstarting at step 7
# Next set the volume of gas available at idle speeds. This is done using the
Volume Control Screw. Please note that the Volume Control Screw controls the AIR volume, not the fuel volume. Screwing it in reduces the air and makes the fuel/air mixture richer. And of course turning the Volume Control Screw out increases the concentration of air and makes the mixture leaner.
Note: The
Volume Control Screw is the smaller of the two adjusting screws, located on the left side of the carburetor just above the Idle Cutoff solenoid (which has a black wire from the positive side of the coil attached to it). The Volume Control Screw is NOT used to set the idle speed - that's the job of the Bypass Screw.
Note: Before setting the Volume Control Screw per the step below, turn the Bypass Screw (the larger one) out a couple of turns, just to get things started.
# Screw the Volume Control Screw in GENTLY until it bottoms out - you don't want to open up the hole. Now unscrew it exactly 2-1/2 turns. This is the initial setting.
Note: Though you want to be careful to not screw the Volume Control Screw in too far, you also want to make sure that it is initially firmly seated before unscrewing it as specified. If you don't start with the Volume Control Screw firmly seated, you may have trouble adjusting the idle with the Bypass Screw, to the point where you may have it turned all the way in and still have the idle too high. This condition will cause stumbling on acceleration if not corrected.
# With the Volume Control Screw out 2-1/2 turns, start the engine and let it warm up. (Make sure the automatic choke is fully open.)
# Now to set the idle. This is done by controlling the volume of air going by the Bypass Screw. The Bypass Screw is larger than the Volume Control Screw and is located a little above and to the left of the Volume Screw.
Note: Again, the idle speed is NOT set with the Fast Idle Adjuster on the top of the throttle arm as it is on the older 28 and 30 series carburetors - though its name (Fast Idle Adjuster) would lead you to think that its used to set the idle.
# As a starting point, turn the idle
Bypass Screw whichever way (most likely out) to set the idle at 850 rpm (fast idle if you don't have a tachometer). For a semi-automatic car, use 900 rpm. (It's far better to have the idle speed too fast than too slow.)
Note: See our Tune-Up Procedure for instructions on how to attach and use a dwell-tachometer.
# With the engine warmed up and the choke fully open, go back to the
Volume Screw and adjust it slowly to obtain the fastest (smoothest running) idle speed (this is usually out - counter-clockwise). You should not turn the screw out much outside the range of 2-3 turns (1/2 turn in/out from the basic 2-1/2 turn out setting).
# Then turn the Volume Control screw back IN (clockwise) very slowly until the engine speed drops by about 20-30 rpm (slightly leaner). If you don't have a tachometer, listen until you can just hear the engine speed start to drop, maybe as little as 1/8th turn on the Volume Screw.
# Go back to the
larger Bypass screw again to reset the idle speed to 850 - 900rpm. (Again, the fast idle is better than too slow. You want it just a little on the rich side. Too slow of an idle speed can gause the engine to overheat.)
