BMW Coupes and Sedans 1970-1988 Repair Guide

Carburetors

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SOLEX 38 PDSI, 40 PDSI, AND 40 PDSIT



See Figures 1 and 2

Before checking or adjusting the engine idle, make sure the vehicle is in a well ventilated area, and the transmission is in NEUTRAL or PARK with the wheels securely blocked for your protection.

  1. Run the engine until it reaches normal operating temperature. Disconnect the air pump outlet hose (leading from the air pump to the exhaust manifold) at the air pump.
  2.  
  3. Adjust the idle speed to 1000 rpm with the idle speed screw.
  4.  
  5. With a CO meter attached to the exhaust pipe of the car, turn the idle mixture adjustment screw to obtain a reading of 0.6-8% CO.
  6.  
  7. Reset idle to 1000 rpm, as necessary, and reconnect the air pump outlet hose.
  8.  



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of Solex PDSI and PDSIT carburetor



Click image to see an enlarged view

Fig. Fig. 2: Turn the mixture control screw to adjust the idle-Solex PDSI and PDSIT type carburetors

SOLEX 32/32 DIDTA



See Figures 3 and 4

Before checking or adjusting the engine idle, make sure the vehicle is in a well ventilated area, and the transmission is in NEUTRAL or PARK with the wheels securely blocked for your protection.

  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. Adjust the idle speed by turning the idle air by-pass control screw until the reading is 850-950 rpm.
  4.  
  5. With a CO meter attached to the exhaust pipe of the car, turn idle mixture control screw to obtain a reading of 0.8-1.2% CO.
  6.  
  7. Refer to the engine specification sticker in the engine compartment and adjust the idle if not within factory range.
  8.  



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of Solex DIDTA type carburetor



Click image to see an enlarged view

Fig. Fig. 4: Adjust idle by turning the idle by-pass screw-Solex DIDTA type carburetor

ZENITH 35/40 INAT TWIN CARBURETORS



Before checking or adjusting the engine idle, make sure the vehicle is in a well ventilated area, and the transmission is in NEUTRAL or PARK with the wheels securely blocked for your protection.

  1. Run the engine until it reaches normal operating temperature. Remove the plugs from the exhaust manifolds and insert the test probes.
  2.  
  3. Remove the air cleaner. You will notice doing this will cause the engine rpm to decrease by about 100 rpm.
  4.  
  5. Disconnect the throttle linkage rod at the ball stud (2) near the rear carburetor. Mark the position of the rod to ease reinstallation.
  6.  

This adjustment requires a carburetor synchronizing meter with 2 caps which replace the effect of the air cleaner on each carburetor, and a CO meter with taps designed to connect with the BMW exhaust manifolds.

  1. Install the 2 caps over the carburetor tops, and connect them to the synchronizer. Now, adjust the 2 idle screws to get an idle rpm between 900-1000, and a reading of 0 on the synchronizing meter. These are the larger screws near the base of each carburetor . If the synchronizing meter shows greater vacuum on one carburetor than on another, adjust the large screws in opposite directions of each other in equal amounts, adjusting the screw of the carburetor with the higher vacuum in the clockwise direction.
  2.  
  3. Adjust the idle mixture screws in or out to bring the CO content in the exhaust under each carburetor to 1.95-2.05% CO. These screws are the small ones next to the large idle screws.
  4.  
  5. If this changes the idle speed, reset the idle screws as described. Then, read the CO meter and, if necessary, readjust the mixture screws as necessary. Continue in this manner until both idle speed (including balance) and mixture are within specification.
  6.  
  7. With the engine off, reinstall the air cleaner, disconnect the exhaust probes and reinstall the plugs. Reconnect the throttle linkage. When reconnecting the throttle linkage,if needed, adjust the length of the connecting rod with the knurled nut so that the rod can be connected without changing the idle speed.
  8.  

 
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