BMW Coupes and Sedans 1970-1988 Repair Guide

Carburetor

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APPLICATIONS



The 1970-71 1600 and 2000 use a single barrel downdraft Solex 38 PDSI carburetor. This unit has a manual choke. The 1970-71 2002, (up to chassis no. 2 583 405) uses a Solex 40 PDSI, which also has a manual choke. The 1970-71 2002 with automatic transmission (up to chassis no. 2 532 752) uses a Solex 40PDSIT unit with a water heated automatic choke.

Later 2002 models use a Solex 32/32 DIDTA carburetor with the water heated choke, to which was added an electric heating element in 1974. Later models also incorporate a float bowl return valve to reduce vapor lock. The 2002Ti uses 2 separate Solex 40 PHH carburetors, which have 2 progressively activated barrels each.

The 2500, 2800, Bavaria, 3000 and 3.0 use 2 Zenith 35/40 2 stage carburetors.

ADJUSTMENTS



Throttle Linkage

Throttle linkage adjustments are generally not necessary except that, if synchronization of the Zenith 35/40 units proves difficult, the adjustable link connecting the 2 throttle linkages should be adjusted to a center-to-center length of 1.5 inches (40mm).

Float Level
38 PDSI, 40 PDSI AND 40 PDSIT
  1. Run the engine until it reaches normal operating temperature. Shut the engine off.
  2.  
  3. Disconnect the fuel feed line from the carburetor.
  4.  
  5. Remove the carburetor top cover and seal.
  6.  
  7. Using a depth gauge, the level of fuel in the bowl should be 0.7-0.8 inches (18-19mm).
  8.  
  9. Adjust, as necessary, by varying the number of or thickness of the seals underneath the float needle valve.
  10.  

SOLEX 38 PDSI AND SOLEX 32/32 DIDTA

The float level cannot be adjusted without the carburetor completely disassembled. Therefore, this adjustment cannot be accomplished without a special sight glass and equipment for adjusting the amount of fuel in the bowl.

ZENITH 35/40

Although the float level is not adjustable, it does depend upon the condition of various parts of the carburetor, especially the gasket used under the float valve. This gasket must be 0.039 inches (1mm) thick.

Fast Idle
2002 MODELS WITH AUTOMATIC CHOKE
  1. Start the engine and allow to reach normal operating temperature.
  2.  
  3. Operate the accelerator rod until the choke plate can be closed by hand. Then, close the choke plate until only 0.25 inches (6.5mm) clearance exists between the plate and the carburetor air horn. This will bring the stop lever into the fast idling speed position. Once this clearance is set, do not disturb the accelerator rod.
  4.  
  5. Using the adjusting nuts at the choke connector rod, adjust the fast idle speed to 2100 rpm. To increase engine speed, increase the rod length. To decrease engine speed, decrease rod length.
  6.  

2500, 2800, BAVARIA, 3000 AND 3.0 MODELS
  1. Make sure the engine is hot, the air cleaner is removed, the carburetors are synchronized, and that the idle speed is 900 rpm.
  2.  
  3. At the distributor there are 2 hoses going to the diaphragm, one advance, and one retard, remove the retard hose which is connected on the distributor side of the diaphragm.
  4.  
  5. Switch OFF the engine and disconnect the choke rod at the rear carburetor.
  6.  
  7. Using a drill bit with a 0.09 inch (2.4mm) diameter, insert it between the lower edge of the choke butterfly and the throttle bore. Open the throttle slightly then close the choke to touch the drill, and pin it against the throttle bore. This will set the fast idle mechanism on the second step. Then, release the choke.
  8.  
  9. Without touching the throttle linkage, start the engine. If the rpm is not 1,400, note the difference.
  10.  
  11. If the speed must be readjusted, stop the engine, open the throttle all the way, and adjust the screw on the choke housing inward to increase the idle or outward to decrease the idle. 1 complete turn equals about 300 rpm.
  12.  
  13. Repeat Steps 4-6 until idle speed is at 1,400 rpm.
  14.  
  15. Open the throttle to open the rear choke. Then repeat Steps 4-6 for the front carburetor.
  16.  
  17. Finally, repeat Step 4 for both front and rear chokes. Both chokes must be set to the proper position while the throttle is held open. Then, both chokes must be held there as the throttle is released. Remove the drill bits, release the chokes, and start the engine. RPM must be 1,800-2,000.
  18.  

Automatic Choke and Unloader
2002 AND 2002A MODELS
  1. Be sure the choke valve shaft will rotate freely in its bore and that the choke cap aligning notch is aligned with the lug on the choke valve housing.
  2.  
  3. Depress the accelerator to allow the choke valve to close under spring tension.
  4.  

The choke valve should close if the ambient temperature is below 68°F (20°C).

  1. If adjustment is needed, remove the choke cap with the water hoses attached.
  2.  
  3. Depress the choke rod (the vertical shaft inside choke housing) downward to its stop and check the choke valve clearance between the choke valve and the throttle bore. The gap should be 0.2-0.3 inches (6-7mm).
  4.  
  5. An adjusting screw and locknut is located under the choke housing and controls the height of the choke rod. Loosen the locknut and move the screw in or out to change the choke valve gap.
  6.  
  7. Reposition of the choke cover on the carburetor. Be sure the choke arm engages the coil spring loop in the choke cover. Align the notch on the cover with the lug on the choke housing.
  8.  
  9. Connect the heating coil wire terminal to the housing.
  10.  
  11. Adjust the fast idle speed to 2000-2200 rpm with the engine at normal operating temperature.
  12.  
  13. With the choke valve set at a gap of 6mm, adjust the choke connector rod nuts to set the fast idle. Shorten the rod to reduce the rpm.
  14.  

2500, 2800, BAVARIA, 3000 AND 3.0 MODELS
  1. Remove the choke cover, leaving the water hoses attached.
  2.  
  3. Open the throttle and close the choke butterfly.
  4.  
  5. Loosen the lockscrew on the pivot unit at the top of the choke rod. Make sure the adjusting screw inside the choke housing points to the high step of the actuating cam.
  6.  
  7. Raise and lower the rod until the gap between the lower end of the rod and the actuating cam is 0.06 inches (1.5mm). Then, tighten the lockscrew and press the clamping ring on the rod up against the pivot unit.
  8.  
  9. Then, push the rod upward and push the actuating cam against the rod.
  10.  
  11. Check the gap between the lower edge of the choke butterfly and the throttle bore. It should be 0.1 inches (3mm). If not, loosen the locknut and turn the adjusting screw on the choke unloader until the dimension is correct. Tighten the locknut and apply sealer.
  12.  

Accelerator Pump

A special metering cup is used to measure accelerator pump stroke and performance. If this is not available, the pump stroke (and fuel delivery) can be adjusted as follows:

On the 2002 models adjust the position of the locknuts on the pump lever. On the 2500, 2800, Bavaria, 3000 and 3

.0 Series adjust by bending the plunger lever (located under the float bowl cover) at the pivot point.

Make sure, before making adjustment, that idle mixture and ignition timing are correct, that the carburetor is clean, and that the plunger and check valves in the accelerator pump system are in good condition.

Idle Stop Solenoid

See Figure 1

The idle stop solenoid prevents any tendency for the engine to run on after the ignition is switched off. The solenoid if non-adjustable, must be replaced if defective. To check operation, pull off the electrical connector when the engine is running. The solenoid is working properly if the engine shuts down. When the connector is replaced, a slight click should be heard. To replace the idle stop solenoid, remove the connector and unscrew the valve assembly from the carburetor. When installing the new solenoid valve, make sure there is a good seal at the taper.


WARNING
Tightening torque for the solenoid is only 2 ft. lbs. (3 Nm).



Click image to see an enlarged view

Fig. Fig. 1: Replacing the idle stop solenoid

Carburetor Dashpot

A dashpot is used to slow the carburetor throttle return while the vehicle engine is above 1800 rpm on carbureted engines. An electrically controlled set of relays and magnetic switches is used to direct engine speeds under a certain rpm.

Operate the engine at 2500 rpm and slowly decrease the speed to approximately 1800 rpm. The dashpot plunger should contact the throttle linkage at the 1700-1900 rpm mark (for 2002 models, 1500 rpm is the minimum). Adjust the dashpot plunger as necessary. If adjustment is needed, turn the screw on the dashpot until it contacts the linkage at the desired rpm.

The plunger must be free of the throttle linkage under 1700 rpm (for 2002 models, 1550 is the minimum) when the engine vacuum is directed through the magnetic valve to the dashpot.

If no vacuum is present at the dashpot hose under 1700 rpm, check the engine speed relay connector. Remove the terminal end from the magnetic valve and increase the engine speed to 2000 rpm. If voltage is present at the terminal, the magnetic valve to the dashpot is defective and should be replaced.

If no vacuum is present at the dashpot hose under 1700 rpm, check the engine speed relay connector. Remove the terminal end from the magnetic valve and increase the engine speed to 2000 rpm. If voltage is present at the terminal, the magnetic switch is defective and if no voltage is present, the speed sensitive relay must be replaced.

Compensation Speed Dashpot
  1. Pull off vacuum hose.
  2.  
  3. Increase engine speed to approximately 2000 rpm, then slowly decrease.
  4.  
  5. At 1800 rpm, the dashpot plunger must touch the carburetor linkage.
  6.  
  7. Adjust if necessary by turning the dashpot after loosening the locknut.
  8.  
  9. Reconnect vacuum hose.
  10.  

If the engine speed is lower than 1700 rpm, but the dashpot plunger does not free the carburetor linkage, check for vacuum to the dashpot. If vacuum is present in the signal line, the dashpot must be replaced.

REMOVAL & INSTALLATION



1600, 2000 and 2002

>Models With Manual Choke

  1. Remove the air cleaner assembly, marking the vacuum lines, breather hoses, and air intake hose for reassembly.
  2.  
  3. Disconnect the fuel feed line at the carburetor and plug.
  4.  
  5. Loosen the clamp screw and clamp, and disconnect the choke cable.
  6.  
  7. Lever off the clamp spring connecting the accelerator rod to the carburetor and disconnect the throttle linkage.
  8.  
  9. Label and remove the vacuum line(s) from the carburetor.
  10.  
  11. Remove the carburetor attaching nuts, and lift the carburetor from the manifold. Remove the flange gaskets and carburetor spacer, taking note of their placement.
  12.  

To install:
  1. Install the carburetor to the manifold using new gaskets and installing the spacer.
  2.  
  3. Reconnect all fuel and vacuum lines. Install the air cleaner and breather hose. Connect the throttle linkage.
  4.  
  5. Adjust the choke cable in the following manner:
    1. Push the choke knob on the dash into the bottom notch.
    2.  
    3. Press the fast idle cam against its stop so that the outer choke cable projects 0.60 inches (15mm) in front of the cable clamp, and tighten the clamp screw in this position.
    4.  
    5. Adjust the idle speed as needed. Tighten the attaching nuts to 7-10 ft. lbs. (9-13 Nm).
    6.  

  6.  

2002 Models With Automatic Choke
  1. Remove the air cleaner assembly, marking the vacuum lines, breather hoses, and air intake hose for reassembly.
  2.  
  3. Disconnect the fuel feed line at the carburetor.
  4.  
  5. Disconnect the electrical cable for the thermostat valve. Drain the radiator of coolant.
  6.  


CAUTION
When draining coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze, and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the retaining screws and lift the choke mechanism cover from the carburetor body.
  2.  
  3. Remove the safety clip from the ball socket at the throttle linkage connection to the carburetor. Press the throttle and down-shift rotary shaft downward and rearward and disconnect the throttle linkage.
  4.  
  5. Label and remove the vacuum line from the carburetor.
  6.  
  7. Remove the 2 carburetor attaching nuts, and lift off the carburetor from the manifold. Remove the flange gaskets and carburetor spacer, taking note of their placement.
  8.  

To install:
  1. Install the carburetor to the manifold using new gaskets and installing the spacer.
  2.  
  3. Reconnect all fuel and vacuum lines. Install the air cleaner and breather hose. Connect the throttle linkage.
  4.  
  5. Insert the automatic choke engaging arm in the eyelet for the bimetallic spring. The choke must be adjusted so that the notch on the choke cover and the projection on the choke housing align. Adjust the idle speed. Tighten the attaching nuts to 7-10 ft. lbs. (9-13 Nm).
  6.  

2002Ti Models
  1. Remove the air cleaner, labeling all hoses.
  2.  
  3. Disconnect the choke cable at the carburetor end and remove the cable at the carburetor end and remove the cable from the bracket.
  4.  
  5. Loosen the dipstick retainer clip.
  6.  
  7. Pull off fuel hoses.
  8.  
  9. Remove the throttle tensioning spring. Remove the 2 carburetor mounting nuts which fasten the mounting bracket for the rotating shaft, and pull the bracket off the manifold studs. Disconnect the rod from the rotating shaft.
  10.  
  11. Remove the remaining mounting nuts and remove the carburetors. Remove all gaskets.
  12.  

To install:
  1. To install, reverse the removal procedure, bearing the following points in mind:
    1. Before installing the carburetor on the right side, position the prong on the choke butterfly lever so it engages with the hole in the linkage of the left hand carburetor by rotating the linkage on the left hand carburetor as necessary.
    2.  
    3. Make sure the torsion spring on the carburetor synchronizing portion of the throttle mechanism is in the proper position.
    4.  
    5. Push the choke knob in to the first notch. Open the choke mechanism on the carburetors all the way. Then, clamp the choke cable snugly in place, making sure the cable sheath does not protrude more than 0.6 inches (15mm).
    6.  

  2.  

2500, 2800, Bavaria, 3000 and 3.0 Models
  1. Drain the radiator of coolant, and remove the air cleaner.
  2.  


CAUTION
When draining coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze, and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Disconnect fuel, vacuum, and water lines.
  2.  
  3. Disconnect and remove the choke cables. Disconnect the fuel return hose at the carburetor, on cars so equipped.
  4.  
  5. Disconnect throttle rod at the carburetor. Remove the carburetor mounting nuts from the studs, and remove the carburetor.
  6.  

To install:
  1. Install in reverse order, noting that the flange gasket must be in position so the smaller opening is situated toward the cylinder head, and the coated side faces down. Synchronize the carburetors and bleed the cooling system when filling it.
  2.  

OVERHAUL



See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the Solex 40 PDSIT carburetor. The Solex 38 PDSIT is similar

Carburetor repair kits are recommended for each overhaul. Kits contain a complete set of gaskets and new parts to replace those that generally deteriorate most rapidly. Not substituting all of the new parts supplied in the kits can result in poor performance later.

Zenith/Solex carburetor repair kits are of three basic types-repair: rebuild, and gasket. The following summarizes the parts in each type

REPAIR KITS:


All jets and gaskets
 
All diaphragms
 
Float needle valve
 
Volume control screw
 
Spring for pump diaphragm
 
Spring for pump diaphragm
 
Pump ball valve
 
Main jet carrier
 
Float
 
Complete intermediate rod
 
Intermediate pump lever
 
Complete injector tube
 
Some cover hold-down screws and washers
 

REBUILD KITS:


All gaskets
 
Float needle
 
Volume control screw
 
All diaphragms
 
Spring
 

GASKET KITS:


All needed gaskets
 

Carburetor overhaul should be performed only in a clean, dust-free area. Disassemble the carburetor carefully keeping look-alike parts separated to prevent accidental interchange during assembly. Note all jet sizes. When reassembling, make sure all screws and jets are tight in their seats. Tighten all screws gradually, in rotation. Do not tighten needle valves into seats. Uneven jetting will result. Use a new flange gasket.

Wash carburetor parts, except diaphragm and electric choke units, in a carburetor cleaner, rinse in solvent, and blow dry with compressed air.

Carburetors have numerous small passages that can be fouled by carbon and gummy deposits. Soak metal parts in carburetor solvent until thoroughly clean. The solvent will weaken or destroy cork, plastic, and leather components. These parts should be wiped with a clean, lint-free cloth. Clean all fuel channels in float bowl and cover. Clean jets and valves separately to avoid accidental interchange. Never use wire or sharp objects to clean jets and passages as this will seriously alter their calibration.

Check throttle valve shafts for wear or scoring that may allow air leakage affecting starting and idling. Inspect float spindle and other moving parts for wear. Replace if worn. Replace float if fuel has leaked into it.

Accelerator pump check valves should pass air one way but not the other. Test for proper seating by blowing and sucking on valve and replace if necessary. Wash valve again to remove breath moisture. Check bowl cover with with straight edge for warped surfaces. Closely inspect valves and seats valves and seats for wear and damage.

Rebuild kits contain complete, step by step disassembly and assembly instructions, for each specific type of carburetor, so they are not included here.

 
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