Tuneup, and Adjustment of the Solex 34 PICT/3 Carburetor
method will also work for the 30PICT/3, 30PICT/4, 31PICT/4,
31PICT/3 and H30/31 carburetors with the
screws in the left side.
Before we begin to adjust the carburetor, the valves, points,
and timing should be set. This is important, and they should
be done in the right order, as you start with a cold engine,
and end with it warm.
topics are addressed in the following in this document (see
links below; for more detail, refer to our Tune-Up
adjustment is always done with the engine stone cold.
inches (0.1 mm)is the factory setting for pre-71 engines.
Some folks find that this is too tight after the engine warms
and use 0.006 inches (0.15 mm). That's engines with a number
starting B..., D..., E..., F..., H..., L..., or a plain
number. (I've always used the factory setting on my H...
engine without any problems.)
inches (.15 mm) is used on 71 and up engines. That's engines
with a number starting AB..., AC..., AD..., AE..., AF...,
AH..., AJ..., AK..., AR..., AS....
aim of the tappet (valve) setting is to provide virtually NO
gap when the engine is at operating temperature.
points are adjusted to .016 inches (0.4 mm). Replace them if
the contacts are pitted or the cam rubbing block is badly
worn. Add a touch of grease to the cam lobs at the same time.
Also pull off the rotor arm and take a look in the centre of
the spindle it rides on. If your distributor has a felt pad
in there, put a few drops of oil (engine oil is fine) on it
to lubricate the distributor drive - don't overdo it though -
a few drops only. Some distributors don't have this felt pad
- in that case skip this procedure.
note that the SIZE of the engine does not matter much when
setting the timing, it's the DISTRIBUTOR design which
determines the settings. The compression ratio also plays a
part – the early low compression engines need a little
more advance, and the later higher compression engines
usually have a little less advance.
usual timing settings are:
engines with single vacuum distributor - 10BTDC. This is set
static - engine off (or at idle with a timing light and the
vacuum line disconnected).
engines with single vacuum distributor - 7.5BTDC. This is
set static - engine off (or at idle with a timing light and
the vacuum line disconnected). In the USA, 68-70 cars with
the H (1500) and B (1600) series engines and a single vacuum
distributor used zero advance – TDC - as an idle
setting, as an early attempt at emissions reduction. This
also reduced the maximum advance at higher revs. Many folks
have found that the 7.5BTDC setting as used outside the USA
works fine (single vacuum distributor).
using the double vacuum distributor (first introduced in
1971) - 5ATDC. This must be set using a timing light, with
the engine idling and the vacuum lines connected so the
retard line can pull in the 5ADTC (After TDC). These
distributors were not used much outside the USA. In other
countries, the 1971 engine had a single vacuum double
advance distributor, which was then fitted to USA cars from
Any VW engine using the Bosch
009 (or other centrifugal distributor) must be set at the
maximum advance with the engine at 3000+rpm, and let the idle
advance fall where it may. The reason for this is that the
009s vary in the total amount of advance they make, and the
maximum advance is more important than idle advance. The
normal setting is a max advance of 30-32 BTDC. Try the 32
degree setting first. If the engine detonates/pings at this
setting, reduce it to 30 degrees. If it still
detonates/pings, use a higher octane fuel. Don't use less
than 30 degrees. The idle advance will then usually fall in
at about 5-10BTDC. Please note that the 009 was designed to
be used on VW industrial engines (generators, compressors and
such, which ran at near constant speeds). VW never used the
009 distributor for any of it's beetle models, and so,
although it will work, you may get flat spots and poor
pick-up when using this distributor.
start the engine and warm it up. Take the air cleaner off the
top of the carburetor (if it's the oil filled type be
careful, you don't want a shoe full of oil) and check that
the choke butterfly is standing vertical. If it isn't, run
the engine some more to make sure it's thoroughly warm, and
check the choke butterfly again. If it is not standing
vertical or almost vertical, the butterfly needs adjusting or
fixing (another topic).
important to set the valves, points, timing and check the
choke (in this order) before setting the carburetor, they all
work together for a smooth running engine.
the 34PICT/3 Carburetor
- this adjustment procedure also works for the other
carburettors with two adjusting screws in the left side –
the 30PICT/3, the 31PICT/3 and the H30/31.
we begin, a short note about the "Haynes VW Beetle &
Karmann Ghia Repair Manual": For those using the earlier
edition of the manual, there is an error on the exploded
views of the 34PICT/3 carburetor. The designations on the
adjustment screws on the left side of the carburetor are
reversed. The larger screw on the top is the Bypass Screw,
and the lower (smaller) one is the Volume Control Screw - not
the other way around as the older Haynes Manual indicates.
Other than that, we have found the Haynes Manual to be an
The correct idle speed is important with the 34PICT/3
carburetor, which is more complicated (and more sensitive)
than the earlier types. It has three separate fuel circuits
in it (only two in older carburetors), and the 850-900 rpm
idle is designed so the airflow through the carburetor is
balanced for the idle circuit fuel flow. That's why it has
both Volume and Bypass screws in the side (the earlier ones
had only Volume screws), located on the left side of the
carburetor. This way the idle speed can be set correctly
using the Bypass screw without touching the screw on the
throttle arm, which has to be set exactly right.
sure that all the hoses are in place and the gasket at the
base of the carburetor is sealing properly (no vacuum leak).
the air cleaner (the carburetor expects it to be there).
on the engine and run it until it is warm, then switch it
first step is to set the throttle plate. Back off the Fast
Idle Adjuster (also called the throttle screw) located at
the top of the throttle arm. You will find the throttle arm
on the left side of the carburetor, connected at the bottom
to the accelerator cable, which runs forward to the
Fast Idle Adjuster is a misnomer - this screw it is NOT used
to adjust the idle speed. The Fast Idle Adjuster works with
the choke to give a smooth idle on a cold engine. As the
choke warms (in concert with the warming engine, hopefully)
the choke butterfly valve in the throat of the carburetor
opens and the Fast Idle Adjuster screw moves down the steps
of the choke fast idle cam, reducing the cold-engine idle
speed down to the warm-engine idle speed. Screwing the Fast
Idle Adjuster screw in more will increase the idle speed,
but doing so messes up the Volume Control and Bypass Screw
adjustments. This destroys the idle geometry, and the car
won't run right.
turn the Fast Idle Adjuster screw in until it JUST touches
the bottom of the stepped cam. Now screw it in another ¼
turn. This sets the throttle butterfly open the required
0.004", so you get the right airflow past the idle and
transfer ports in the inside of the carburettor throat. You
can now use the Bypass Screw (read on) to set the idle speed
correctly. From this point on, leave the Fast Idle Adjuster
set the idle mixture. This is done using the Volume Control
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.
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.
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 full turns. This is the initial setting.
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
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 – pull and release the throttle arm if needed so
the stepped cam rotates and the Fast Idle Adjuster is
sitting at the bottom of the stepped cam.)
to set the idle. This is done by using 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.
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.
a starting point, turn the larger 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 a little
fast than too slow.)
See our Tune-Up Procedure for
instructions on how to attach and use a dwell-tachometer.
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 usually need to 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).
turn the Volume Control screw back IN (clockwise) very
slowly until the engine speed drops by about 20-30 rpm. 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.
back to the larger Bypass screw again to reset the idle
speed to 850 - 900rpm. (Again, a little fast is better than
too slow. Too slow of an idle speed can cause the engine to
overheat when you stop at the lights after a good run, as
the cooling fan will not be producing enough cooling air to
cope with the residual heat in the engine.)
If you find it difficult or impossible to make these
settings, it is possible that you could have stripped
threads on any of these adjusters, a damaged hole for the
tapered screw, or a damaged needle valve or O-ring.
is also possible that you have a vacuum leak (i.e., leaking
of air into the intake manifold). If there are any
holes/gaps in the manifold or at any of the connection
points, then air can be sucked into the manifold, causing
the fuel-to-air mixture to become too lean. This can cause
(among other things) adjustment of the carburetor
impossible. See our Discussion
of Air Inleakage, which includes diagnosis and repair.
it - you're done. Your engine should be purring like a
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