Volkswagen Air-Cooled 1970-1981 Repair Guide

Carbureted Vehicles

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A carburetor adjustment should be performed only after all other variables in a tune-up have been checked and adjusted. This includes checking valve clearance, spark plug gap, breaker point gap and/or dwell angle, and ignition timing. Prior to making any carburetor adjustments, the engine should be brought to operating temperature (122-158ordm;F oil temperature) and you should make sure that the automatic choke is fully open and off of the fast idle cam. Once you have performed all of the preliminary steps, shut off the engine and hook up a tachometer. Connect the hot lead to the distributor side of the ignition coil and the ground wire to an engine bolt or other good metal to metal connection. Keep the wire clear of the fan.

An improper carburetor adjustment may have an adverse effect on exhaust emission levels. If any doubt exists, check your state laws regarding the adjusting of emission control equipment.

SOLEX 30 PICT-3



1970 TYPE 1 AND TYPE 2 MODELS
  1. Start the engine and bring it to operating temperature. Make sure the car is in neutral.
  2.  
  3. Using the idle speed (bypass) screw, adjust the idle speed to that specified in the "Tune-Up Specifications" chart.
  4.  

The bypass screw adjustment is the only adjustment that should be made to 30 PICT-3 carburetor. Do not attempt to adjust the mixture or idle speed by turning the throttle valve adjustment screw, as increased exhaust emissions or poor driveability would result. The bypass screw is the larger adjustment screw.

SOLEX PICT-3 (1971-74 TYPE 1 MODELS, 1971 TYPE 2 MODELS) AND SOLEX 34 PICT-4 (1973-74 TYPE 1 CALIFORNIA MODELS)



See Figure 1

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Fig. Fig. 1: Solex 34 PICT-3 and 34 PICT-4 idle adjustment locations (30 PICT-3 similar)

  1. Start the engine and bring it to operating temperature. Make sure the car is in neutral.
  2.  
  3. Shut off the engine. On 1971 models, turn out the throttle valve adjustment screw until it clears the fast idle cam. Then turn in the screw until it makes contact with the fast idle cam. Finally, turn the throttle valve adjusting screw in another one-quarter turn.
  4.  
  5. Slowly turn in the idle mixture (volume control) screw until it bottoms. Then, carefully counting the complete revolutions of the screwdriver, turn it out 2 1 / 2 to 3 turns.
  6.  
  7. With a tachometer connected to the engine as previously described, start the engine.
  8.  
  9. Using the idle speed (bypass) screw, adjust the idle speed to specifications. Then, using the idle mixture (volume control) screw, adjust until the fastest idle is obtained. Observing the tachometer, turn the volume control screw until the engine speed drops by 20-30 rpm.
  10.  
  11. Finally, using the bypass screw, adjust the idle to specifications.
  12.  

SOLEX 34 PDSIT-2/3 TWIN CARBURETORS



(1972-74) TYPE 2 MODELS



Periodic Adjustment See Figure 2

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Fig. Fig. 2: Type 2 twin carburetor set-up adjustment locations-34 PICT-2 (left carburetor shown)

  1. Start the engine and bring it to operating temperature (122-158ordm;F oil temperature). Make sure the car is in neutral and the parking brake firmly applied.
  2.  
  3. Using the central idle speed adjusting screw (4) on the left carburetor, adjust the idle speed to that listed in the "Tune-Up Specifications" chart.
  4.  

3a. If a CO meter/exhaust analyzer is available, adjust the carbon monoxide (CO) level to 1-3% CO using the central mixture control screw (5) also on the left carburetor.

3b. If a CO meter is not available, the following procedure is used: First, slowly turn the central mixture control screw (5) in (clockwise) until the engine speed drops noticeably, then turn the screw out (counter-clockwise) until maximum idle speed is attained. Next, turn the screw in once again until rpm drops 20-50 rpm. Finally, turn the screw out 1 / 4 turn.

  1. Recheck the idle speed, and adjust as necessary using the central idle speed adjusting screw (4) on the left carburetor.
  2.  
  3. If a satisfactory idle cannot be obtained using this procedure, proceed to "Basic Adjustment."
  4.  

Basic Adjustment See Figures 3, 4 and 5

Click image to see an enlarged view

Fig. Fig. 3: On 34 PDSIT-2/3 carburetors, the throttle valve closing gap (A) must be 0.004 in.



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Fig. Fig. 4: Volume control screw location (arrow) in the carburetor throttle bodies of 34 PDSIT-2 and PDSIT-3 carburetors



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Fig. Fig. 5: Terminal connection location (arrow) for the idling cut-off valve of both right and left carburetors

Whenever a carburetor has been removed for service, or if a new or rebuilt carburetor has been installed, a basic carburetor adjustment should be performed.

The throttle valve setting (distance "a") must be 0.004 in.

An exhaust analyzer/CO meter and tachometer is required for this adjustment.

  1. Check the synchronization of the carburetors as outlined under "Balancing Multiple Carburetor Installations."
  2.  
  3. Disconnect the throttle linkage rod from the right carburetor.
  4.  
  5. Disconnect the vacuum retard hose from the distributor.
  6.  
  7. Disconnect the cut-off valve wire at the central idling system. Disconnect and plug the left side air pump hose (1973-74 models).
  8.  
  9. Turn the idle volume control screws (6) in on both carburetors until they contact their seats.
  10.  


CAUTION
Do not force the screws or the tips may become distorted.

Then, turn both screws out exactly 2 1 / 2 turns.

  1. Start the engine and bring it to operating temperature (122-158ordm;F oil temperature). Set the idle speed to 500-700 rpm by equally adjusting both volume control screws (6).
  2.  
  3. Disconnect the wire from the electromagnetic idling cut-off valve (smaller of the two valves) at the left carburetor and note the decrease in idle speed. Then, repeat this operation for the right carburetor. The idle speed drop should be equal for both sides. If not, readjust the volume control screws accordingly.
  4.  
  5. Connect the wire for the cut-off valve at the central idling system. Unplug, and connect the left air pump hose. Connect the vacuum retard hose.
  6.  
  7. Take the engine through the upper rpm range for a few quick bursts. Then, adjust the idle speed to specifications as outlined under steps 2-5 of "Periodic Adjustment."
  8.  

Synchronizing Twin Carburetors See Figure 6

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Fig. Fig. 6: Using an airflow meter to synchronize the carburetors on a twin carburetor set-up

If a carburetor has been removed or disassembled, or if any part of the linkage has been repaired, the carburetors must be synchronized prior to performing any idle adjustments. To synchronize the carburetors, a special instrument is used to measure air flow, such as the UniSynreg; or Auto-Synreg;. This commonly available device measures the vacuum created inside the carburetors and provides an index for adjusting the carburetors equally. In order to use the air flow gauge on the 34 PDSIT carburetors, a special diameter adaptor (or a small frozen juice can with both ends removed) must be used.

  1. Disconnect the linkage connecting rod from the lower socket of the right carburetor. Without moving the throttle from its closed position, you should be able to snap the linkage connecting rod back onto the socket for the right carburetor. If the ball and socket at the right carburetor do not align perfectly, for 1972 models, adjust with the synchronizing screw (1) at the left carburetor; on 1973-74 models, adjust the length of the connecting rod on the right carburetor until the rod can be snapped onto the socket without disturbing the throttle from its fully closed position. Connect the linkage and hook up a tachometer.
  2.  
  3. Remove the air cleaner ducts from the tops of both carburetors, taking care to leave the central idle system connecting hose (3) and left end piece (2) connected.
  4.  
  5. Start the engine and bring it to operating temperature (122-158ordm;F oil temperature). Make sure the choke flaps are fully open. Using the air flow meter, balance the carburetors using the synchronizing screw (1) on the left carburetor on 1972 models or the connecting rod on the right carburetor on 1973-74 models. Balance the carburetors with the engine running at 2,000-3,000 rpm.
  6.  
  7. Adjust the idle speed to specifications.
  8.  

 
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