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Technical Articles

The VW Carburetor System

Originally written by Rob Kuhn

Between 1961 and 1974, VW used a variety of carburetors. They all work on the same general principle.

The fuel system consists of a front mounted fuel tank connected through a line to the fuel pump. An eccentric cam on the distributor drive shaft operates the mechanical fuel pump which delivers fuel to a downdraft type carburetor (ie: Solex).

All carbureted VW’s use an oil bath type air cleaner (unless yours has been replaced with an aftermarket paper/foam element type).

There has been six different Sloex downdraft carburetors used between 1961 and 1974. Below is a brief description of each:

28 PICT 1961 – 1963

This was the first VW carburetor equipped with an automatic choke. A vacuum piston opens the choke butterfly slightly when the engine starts. This model has a power fuel system which means that it draws fuel directly from the float chamber under full load and high speed conditions.

28 PICT-1 1964 and 1965

This model is very much the same as the 28 PICT except that a vacuum diaphragm replaces the vacuum piston. This model also did not have a power fuel system.

30 PICT-1 1966 and 1967

This model is similar to the 28 PICT-1 except that it has a larger venturi. This model also does not have a power fuel system.

30 PICT-2 1968 and 1969

This model is like the 30 PICT-1 except that it does have a power fuel system.

30 PICT-3 1970

This model is similar to the 30 PICT-2 except that redesigned idling permits the throttle to completely close at idle, while idle speed is controlled by air bypass around the throttle.

34 PICT-3 and 34 PICT-4 1971 – 1974

These two carburetors are similar to the 30 PICT-3 except a bypass mixture cutoff valve replaces the pilot jet cutoff valve, and the venturi is larger. Although all 1971 thru 1974 carburetors are 34 PICT types, differing choke parts prevents interchangeability. On the 1972 models, preheating was improved and so a new element was used. These are identified with 60 on the choke cover.

Removal and Installation.

  1. Remove the air cleaner.
  2. Pull the fuel line off. Place a rag under the fuel inlet of the carburetor, this will help catch any fuel that might drip out. You might have to clamp the fuel line.
  3. Remove the vacuum line.
  4. Disconnect the electrical connections (be sure to label them) –
    • 1961 – 1970: Disconnect the automatic choke and pilot jet cutoff valve.
    • 1971 – 1974: Disconnect the automatic choke and the bypass mixture cutoff valve.
  5. Disconnect the accelerator cable from the throttle linkage.
  6. Remove both carburetor mounting nuts.

The carburetor can now be removed/lifted from the intake manifold. Installation is in the reverse order, be sure to use a new gasket that goes between the carburetor and the intake manifold.


  1. Remove the five (slotted) screws securing the upper part of the carburetor to the body and lift the top off.
  2. Pull out the float retainer and the float.
  3. Unscrew the float needle valve from the upper part of the carburetor.
  4. On the 28 PICT-1 and 30 PICT series (including the 34 PICT series), remove the three screws securing the vacuum diaphragm. Remove the spring and diaphragm.
  5. Remove the three screws that hold the automatic choke.
  6. Remove the …
    • Retainer.
    • Spacers.
    • Choke.
    • Plastic cap.
  7. Unscrew/remove the air correction jet.
  8. On the …
    • Solex 28 PICT, 28 PICT-1, 30 PICT-1, 30 PICT-2 and 30 PICT-3, unscrew the pilot cutoff valve.
    • Solex 34 PICT-3 and 34 PICT-4, unscrew the bypass mixture cutoff valve.
  9. Now remove the the main jet plug, seal and main jet.
  10. On the …
    • Solex 28 PICT, 28 PICT-1, 30 PICT-1 and 30 PICT-2, remove the idle mixture screw and spring.
    • Solex 30 PICT-3, 34 PICT-3 and 34 PICT-4, remove the air bypass screw.
      CAUTION – Do not remove the volume control screw near the air bypass screws. These are factory preset and must not be removed or adjusted.
  11. Remove the cotter pin.
  12. Now remove the four screws that hold the accelerator pump cover. Remove the cover, diaphragm and spring.

Viola! That’s it! You’ve just disassembled your Solex. Pretty simple, eh?


Just about all auto part stores have some sort of carburetor cleaning solvent. Some come in the form of a spray can while others, the kind I use and recommend, come in a can (about the size of a paint can) which has a little basket inside the can in which to submerge your parts. A company called Gunk makes something called “Carburetor Dip”, or at least they used to (it might be called something else now) which is what I use. It comes in a paint can with a small basket in which I can submerge my parts.

Use compressed air to dry the parts. If you don’t have access to an air compressor, most auto part stores and electronic part stores (ie: Radio Shack) sell compressed air in a can which also works fine. Aside from the automatic choke, clean all the parts. Use a clean cloth to wipe the choke. To clean the jets (and all the drillings in the carb body), I recommend using compressed air rather than a piece of wire or pins. You can run the risk of enlarging the holes.


It’s in the reverse order in which you took it apart.

I recommend using a rebuild kit when it comes to reassembling your Solex. They don’t cost all that much, about $10.00 (US) the last time I checked, and they include everything but the float and jets. It’s a good investment.

30 PICT-2 Carburetor
30 PICT-2 Carburetor


1 Carburetor upper half screw 13 Diaphragm spring 25 Spring
2 Spring washer 14 Diaphragm 26 Pilot jet cutoff valve
3 Carburetor upper half 15 Gasket 27 Circlip
4 Float needle valve 16 Accelerator cable return spring 28 Fillister head screw
5 Needle valve washer 17 Carburetor lower half 29 Pump cover
6 Retaining ring screw 18 float and pin 30 Pump diaphragm
7 Retaining ring 19 Float pin bracket 31 Diaphragm spring
8 Retaining ring spacer 20 Air correction jet 32 Cotter pin
9 Automatic choke 21 Main jet plug 33 Washer
10 Plastic cap 22 Plug seal 34 Connecting rod spring
11 Fillister head screw 23 Main jet 35 Connecting rod
12 Diaphragm cover 24 Volume control screw 36 Accelerator pump injector tube


Carburetor Flat Spots

By-pass Orifices

The drillings (orifices) in the throttle chamber close to the throttle plate are known as “by-passes”. The purpose of these is to ensure a smooth transfer from idle to normal speeds. (i.e. Transfer from the fuel provided by the idle port to the fuel provided by the main jet discharge arm). As an example, the 34 Pict 3 has three by-pass orifices that operate by a step effect as the throttle plate passes each one. By virtue of the distance of the throttle plate from each drilling, increasingly less fuel is discharged from each of the by-pass orifices as the throttle plate opens. This allows more fuel to be discharged from the by-passes until the main jet discharge arm begins to supply more fuel, and less fuel when the discharge arm is giving a full supply of fuel.

Throttle Body Image

Flat Spot Conditions (hesitation in acceleration)

A “flat spot” usually occurs when accelerating for the following two reasons:

  1. The throttle plate has passed the by-pass orifices and fuel is not yet being drawn from the main jet discharge arm. In this situation the throttle plate is opening wider and less fuel is being drawn from the by-pass orifices.
  2. Oppositely, the throttle plate has not yet reached the by-pass orifices.

Remedies for the Flat Spot Conditions

In the two “flat spot” conditions above the following may be done to remove the condition:

  1. In condition No. 1 above, a hole drilled in the edge of the throttle plate will enable the orifices to operate with a wider opening of the throttle plate, and it also will allow the throttle plate to be closed slightly more when idling.
  2. In condition No. 2 above, Filing a small amount off of the lower edge of the throttle plate (beveling the edge) on the side nearest to the orifices will bring the edge of the throttle plate nearer to the first of the by-pass orifices.

Fan Belt Adjustment, Type 1 Engine

APPLICATION: This should apply to all air-cooled Volkswagens fitted with the upright fan housing Type 1 engine. This would be all Beetles and Super Beetles, all Karmann Ghias, all Things (181s), and Buses through 1971.

TOOLS NEEDED: Hefty screwdriver; wrench to fit alternator/generator pulley nut. This nut was 19mm on my Karmann Ghia.

Adjustment for the fan belt tension on a Type 1 engine is kind of goofy compared to more modern cars. Since the generator/alternator is in a fixed place on this engine, VW had to provide for adjustment of the fan belt another way. They did this with shims. The alternator/generator pulley is really two separate halves. To adjust the belt tension, the pulley nut is removed and shims are added to or subtracted from the space between the pulley halves. Adding shims decreases belt tension, and subtracting shims increases belt tension.

The belt should be at least tight enough so that turning the generator/alternator pulley with a wrench also turns the engine. If it is too loose, turning the pulley will just turn the generator/alternator shaft while the belt slips on the pulley. In this particular engine, proper fan belt tension is vital, since any belt slipping reduces the amount of cooling air that is supplied by the fan to the engine. Of course, having the belt too tight can cause premature wear on the alternator/generator bearings.

When depressed by thumb pressure midway between the two pulleys, the belt should give approximately 1/2″.

If the tension is more or less than this, it must be adjusted to bring the tension into specification.

To adjust the tension, first you must remove the pulley nut. Observe that there are some notches in the front half of the pulley (front is front). Take your big screwdriver and stick that in one of the notches so you can hold the pulley stationary while using your wrench to loosen the pulley bolt. Once you have the bolt off, you see a metal bell-looking thing, and under that are some shims. Remove all that stuff and then remove the rear pulley half. Then add or subtract shims as required to bring your belt tension into specification.

The problem with this adjustment method is that you have to guess how many shims you need to add or subtract, then put it all back together and check it. If it’s still not correct, then you have to go back and do it again. This is not the best design, but I have to admit it works.

Once you’ve got the belt adjusted correctly, make sure you tighten the alternator/generator pulley nut sufficiently, and you’re done.

— Sean Bartnik, February 10, 1998

Valve Adjustment

APPLICATIONS: Volkswagen Type 1 engine, specifically the 1600cc version. This probably applies to other Type 1 engines as well and the theory is similar for the Type 4 engine, but I write this after doing a valve adjustment on a 1974 Karmann Ghia convertible, so take that for what it’s worth.

Valve adjustment is a regular maintenance item for the air-cooled Volkswagen Type 1 engine. It must be done every 3000 miles. What you are doing is adjusting the clearance between the rocker arms and valve stems.

TOOLS NEEDED: feeler gauge with .006″ blade; large screwdriver; medium sized flat-blade screwdriver; 13mm wrench, preferably box-end; ratchet with appropriate socket to fit the nut on the generator/alternator pulley; bottle of White-Out; two new valve cover gaskets; tub of wheel bearing grease; fine-grit sandpaper or steel wool; a straight-edge of some kind.

Your valves should be adjusted only when the engine is stone cold. So, the night before you plan to do the job, park the car where you will be working the next day and let it sit overnight. You can’t start the engine to move it before you adjust the valves.

OK, the first step to adjusting your valves is to put the transmission in neutral. This way, you will be able to turn the engine over by hand. Now, look at your crankshaft pulley. You will see the timing notch(es) cut into the rim of the pulley. On the rear pulley face (rear is rear) you should see a dot near the edge. This dot is pressed into the pulley face. It marks TDC (top dead center) for cylinder number 1. What you want to do is take your straight-edge and use it to make a mark on the opposite end of pulley, exactly 180 degrees from the dot. Make the mark with White-Out. Now you should have two marks on the pulley, one pressed in from the factory, and one made with White-Out, and both marks should be exactly opposite each other.

OK, now take your ratchet with socket that fits the alternator pulley nut and put it on the alternator pulley nut. If your pulley nut is too big for your collection of sockets, use an adjustable wrench. You are going to turn the engine over with this ratchet/wrench. Turn the engine counterclockwise so that the factory dot on the pulley lines up evenly with the seam in the crankcase (visible above the pulley). Pull off the distributor cap and verify that the rotor is in position to fire the #1 spark plug (see which wire the rotor is sitting underneath, and make sure it goes to #1).

(If turning the alternator pulley nut does not turn the engine but simply turns the alternator pulley, your drive belt is too lose. You tighten it by remove the pulley nut, the shims stored underneath it, and the rear pulley half, then add some of the shims between the two pulley halves until the tension is within specifications. Check your manual for exact specifications.)

If it does not point to the number 1 cylinder, rotate the engine counterclockwise until it does. When the rotor lines up with the number 1 cylinder spark plug wire, the dot or mark on the pulley should line up with the seam in the crankcase. Don’t expect the rotor alignment to be exact, but it will be very close (remember that the spark is not usually fired exactly at top dead center).

OK, so your situation is now that you have one of the two marks on the pulley (should be the factory dot) aligned with the seam in the crankcase and the rotor is roughly pointing to the number 1 cylinder firing position. You are now at top dead center for cylinder number 1.

Now you have to crawl under the right side of the car and remove the valve cover from the right side bank of cylinders. The one closest to the front of the car is number 1, and the other is number 2. For confirmation, the cylinder numbers are stamped in the tin next to the spark plugs. You will see that the valve cover is held on with a large wire bail. You need to use your large screwdriver to pry the bail down. Once the bail is down, you can simply pull the valve cover off. If you’re lucky, the cork gasket will all come off in one piece. If you’re not lucky and someone used some kind of gasket sealer on the valve cover gasket, you will have a really fun time with it. Anyway, we can worry about that later.

Once you have the valve cover off, observe the scene before you. You are peering into your cylinder head. You see the rocker arm assembly, with four rocker arms, four pushrods, and four valves with valve springs. You see that the pushrods push on the rocker arms, which push on the valves, opening them. When the pushrods stop pushing on the rocker arms, the valve springs close the valves. What pushes on the pushrods is the camshaft, pushing on the solid valve lifters, which push on the pushrods, etc.

Look at the valves for #1. There are two, the front-most ones. They should both be closed completely, and in the same position. If one is in a different position than the other, you are not at TDC for that cylinder, so go back over the above steps and find out where you messed up. Wiggle the rocker arms. You should feel a little bit of movement. You are going to be adjusting the clearance between the rocker arm and the valve stem to .006″, which is a pretty small clearance.

OK, so get your feeler gauge out and whip out the .006″ blade. You will notice that it’s quite thin. What you want to do is push the rocker arm in at the bottom and make sure the pushrod is fully seated in it, so take up all the slack. Then stick your .006″ feeler gauge into the gap between the valve stem and the rocker arm. Make sure you stick it in straight or you will get a false reading. You should be able to feel it slide through the gap with only a slight bit of friction. If it’s hard to push through or grabs, then the valve is tight and requires adjustment. Likewise, if it just slips right through with no friction at all, the valve is loose and also requires adjustment.

To adjust, observe the valve end of the rocker arm. You will see what looks like a screw surrounded with a 13mm nut. The nut is a locknut, so what you do is get your 13mm wrench on it and loosen the locknut. Then you will see that the screw in the middle is free to turn, so get your medium screwdriver and turn it whichever way you need to turn it to achieve a .006″ gap. Then tighten the locknut while holding the screw stationary with your screwdriver. Then re- check your adjustment to make sure tightening it hasn’t changed the adjustment. Once you get that valve adjusted to .006″, then do the other valve for #1 exactly the same way. It’s the one directly behind the one you just did. As a note, the two valves at the very front and very rear of the cylinder head are exhaust valves, and the two inner ones are intake valves.

Now, once you’ve completed both valves for number 1, then you have to crawl back out from under the car and rotate the engine counterclockwise 180 degrees. That is, use your ratchet on the alternator pulley again, and turn the engine counterclockwise until the other mark on the crankshaft pulley is aligned with the crankcase seam. This will bring the number 2 cylinder to TDC, and that’s the one immediately to the rear of the number 1 cylinder. Note why this is: The firing order for the cylinders is 1-4-3-2, and the engine normally rotates clockwise. So when you rotate the engine counterclockwise, you are essentially following the order 1-2-3-4.

Now, you adjust the valves for the number 2 cylinder the same way you did number 1. Then when you are done there, you get out and rotate the engine another 180 degrees counterclockwise, which brings cylinder number 3 into position for the valve adjustment. Number 3 is on the left side of the engine, and is the front-most cylinder. So naturally you will have to remove the valve cover on the left side before adjusting the valves on number 3. Leave the valve cover off on the right side for now, we’ll put both of them back on later.

Once you are done with number 3, rotate the engine another 180 degrees counterclockwise, bring cylinder 4 to TDC for valve adjustment. Once you are done with that, if you’re uneasy, you can rotate the engine 180 degrees at a time and double check all your valve adjustments in the same order you adjusted them.

Now, keep track of which valves (if any) were tight, meaning had a gap smaller than .006″, where the feeler gauge wouldn’t fit through. You want to see if the same valves are tight next time you do a valve adjustment. If they are, you may have valves that are stretching and getting ready to break, so it would be good to remove the cylinder heads and have the valve gear inspected. You must remove the engine before removing the cylinder heads, but preventive maintenance is better than having a valve stretch and then break on you, which will mandate a complete engine rebuild. Typically, the #3 exhaust valve first exhibits these symptoms, so keep a special eye on that one.

OK, well now you’re done adjusting your valves and you are ready to re-install the valve covers. First you need to remove the remains of the old gaskets from the valve covers and cylinder heads. If someone used a gasket sealer on them, especially on the cylinder head side, you will have a real time getting it off, but whatever you do, you must get all the gasket remnants off.

Once you’ve done that, run your finger over the gasket sealing surfaces on the heads. They should be very smooth and not rough with accumulations of crud. If they are rough, they need to be smoothed down or the new gaskets will leak. Used some steel wool to go over the sealing surfaces and smooth them down. Go around the sealing surfaces on both heads, and get them nice and smooth with no crud chunks remaining.

Now you need to clean the gasket remnants from the valve covers. Do it the same way. Get the sealing surface there smooth as well. Don’t forget to clean the oil out of the valve cover as well. Then get one of your new gaskets out (clean your hands a bit first, get all crud chunks off your hands before handling the gaskets) and apply a very light film of wheel bearing grease to one side. Just dip you finger in the grease a little and smooth it on one side of the gasket. You don’t need a lot, just enough to coat it with a light film.

Lay the gasket in the valve cover, coated side down. Then coat the other side the same way. Do not use any gasket sealer or adhesive, it’s not needed if you cleaned the sealing surfaces properly. Once you have the gasket greased, put the valve cover back on the head, make sure it’s seated correctly, and then use your large screwdriver to pry the bail back up to the notch in the middle of the valve cover. Repeat this with the other side. Once again, make sure the valve cover is seated properly on the head or it will leak.

Put the distributor cap back on, remove your socket/ratchet from the alternator pulley and fire it up! It should run at least as well as it ever did 🙂 . If it runs much much worse and your valves were all way out of spec, you may have done it incorrectly, and you should go back and re-read the instructions carefully to see where you goofed. I found when I did the Karmann Ghia, the valves were all in spec except the number 3 exhaust valve, which was a little tight. I will have to keep an eye on that one.

Also check to make sure your valve cover gaskets are not leaking. If they are, pull them off again and fix them up right so they don’t leak.

I think that’s all there is to it, so good luck. I probably made it out to sound a lot harder than it is, once I got going it didn’t take very long at all to do all four cylinders.

— Sean Bartnik, September 24, 1997