Basic Tuneup, and Adjustment of the Solex 34 PICT/3 Carburetor

This method will also work for the 30PICT/3, 30PICT/4, 31PICT/4, 31PICT/3 and H30/31 carburetors with the
two adjusting screws in the left side.


Note: 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.

These topics are addressed in the following in this document (see links below; for more detail, refer to our Tune-Up Procedures).


Setting the Valves

Valve adjustment is always done with the engine stone cold.

0.004 inches (0.1 mm) is the factory setting for pre-71 engines. That includes engines with a number starting B..., D..., E..., F..., H..., L..., or a plain number. Some folks find that this is too tight after the engine warms and use 0.006 inches (0.15 mm). (I've always used the factory setting on my H... engine without any problems.)

0.006 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....

The aim of the tappet (valve) setting is to provide virtually NO gap when the engine is at operating temperature.


Setting the Points

The 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.


Setting the Timing

Please 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.

The usual timing settings are:

  • 1200 engines with single vacuum distributor - 10BTDC. This is set static - engine off (or at idle with a timing light and the vacuum line disconnected).

  • 1300/1500/1600 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).

  • Engines using the double vacuum distributor (first introduced in 1971) - 5ATDC, as a further atempt to reduce emissions at idle. 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 1974 onwards.

Note: ANY, repeat ANY VW aircooled 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 28-32 BTDC. Try the 32 degree setting first. If the engine detonates/pings at this setting, reduce it to 30 degrees and try again. If it still detonates/pings at 28 degrees, use a higher octane fuel. Don't use less than 28 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). It was never designed for engines used on the road with their continually varying load and rpms. 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. Because it actually has less total advance than most vacuum distributors which can provide up to about 40-42 degrees when the engine needs it, the 009 will usually have worse fuel economy too.


Checking the Choke

Now 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).

It's 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.


Setting the 34PICT/3 Carburetor

Reminder - 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.

Before 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 excellent resource.

Note: 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.

  1. Make sure that all the hoses are in place and the gasket at the base of the carburetor is sealing properly (no vacuum leak).

  2. Install the air cleaner (the carburetor expects it to be there).

  3. Turn on the engine and run it until it is warm, then switch it off.

  4. The 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 accelerator pedal.

    Note: Fast Idle Adjuster is something of 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 lock step 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.

  5. Slowly 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 screw alone.

  6. Next set the idle mixture. This is done using the Volume Control Screw.

    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 used to set the idle mixture.

    Note: Before setting the Volume Control Screw per the step below, turn the Bypass Screw (the larger screw in the left side) out 2.5 full turns, which is the initial setting.

  7. Screw the Volume Control Screw in GENTLY until it bottoms out - you don't want to open up the hole. Now unscrew it exactly 2.5 full 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.

  8. 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 – 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.)

  9. Now to set the idle speed. 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.

    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.

  10. As 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.)

    Note: See our Tune-Up Procedure for instructions on how to attach and use a dwell-tachometer.

  11. With the engine warmed up, idling at about 850rpm, 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).

  12. Then 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.

  13. Go 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.)

    Note: 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.

    It 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.

That's it - you're done. Your engine should be purring like a kitten!

* * * * *






Design by Erin