Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Carburetor

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Three types of carburetor are used on Subaru vehicles. All 1.2L engines use a DFC-328 carburetor; 1.6L engines use a DCP-306 carburetor and 1.8L engines use a DCZ-328 carburetor.

The carburetor supplies the correct mixture of fuel and air to the engine under varying conditions. Despite their complexity in design, carburetors function because of a simple physical principle (the venturi principle). Air is drawn into the engine by the pumping action of the pistons. As air enters the top of the carburetor it passes through a venturi, which is nothing more than a restriction in the throttle bore. The air speeds up as it passes through the venturi, causing a slight drop in pressure. The pressure drop pulls fuel from the float bowl through a nozzle into the throttle bore, where it mixes with the air and forms a fine mist which is distributed to the cylinders through the intake manifold.

The carburetor uses a progressive linkage between the primary and secondary circuit. For optimum performance plus fuel economy, the secondary circuit of the carburetor is used only at high engine rpm. Normal low speed operation is handled by the primary circuit.

On later models, the carburetor is provided with a coasting bypass system which helps control exhaust emissions during deceleration.

An automatic control choke is used on all carburetors. The automatic choke and a throttle chamber are heated by engine coolant to prevent throttle bore icing, help the engine start and run well in the coldest conditions.

The basic systems of the carburetor are:

  1. The float system
  2.  
  3. The primary side
    1. Slow system
    2.  
    3. Main system
    4.  
    5. Accelerator pump
    6.  
    7. Power system
    8.  
    9. Choke system
    10.  
    11. Slow float shutoff system
    12.  

  4.  
  5. Secondary side
    1. Step system
    2.  
    3. Main system
    4.  

  6.  
  7. Coasting bypass system.
  8.  

If you are planning to clean, rebuild or replace your carburetor, be sure you understand what is necessary. Read all instructions, have all parts and tools on hand and keep everything as clean as possible. Remember that gasoline mileage and performance depend on how well you do the job.

ADJUSTMENTS



Automatic Choke Mechanism

See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Throttle valve measurement-1.2L carbureted engine



Click image to see an enlarged view

Fig. Fig. 2: Throttle valve measurement-1.6L and 1.8L carbureted engines

  1. With the carburetor removed from the engine, set the fast idle cam adjusting lever on the fourth highest step of the fast idle cam.
  2.  
  3. Check to be sure that the choke valve is fully closed.
  4.  
  5. Measure the clearance between the lower edge of the primary throttle valve and the bore.
  6.  
  7. Measurement should be as follows:

    DFC-328: 0.0303 in. (0.77mm)
     
    DCZ-328: 0.0472-0.0587 in. (1.20-1.49mm)
     
    DCP-306: 0.0386-0.0528 in. (0.98-1.34mm)
     

  8.  
  9. If not within specification, turn the fast idle adjusting screw.
  10.  

Vacuum Break Opening Angle

See Figures 3 and 4

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Fig. Fig. 3: Using a finger to hold the choke valve closed-1.2L carbureted engine



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Fig. Fig. 4: Vacuum break opening angle adjustment-1.6L and 1.8L carbureted engines

  1. Move the throttle lever while lightly holding the choke valve with your hand, to keep it fully closed. Release your hand to make sure the choke valve is fully closed.
  2.  
  3. With the choke valve closed, connect a portable vacuum pump to the vacuum break diaphragm and continue to apply vacuum pressure until the diaphragm shaft moves a complete stroke toward the diaphragm.
  4.  
  5. Measure the clearance (R) while lightly holding the choke valve with your hand. Clearance should be as follows:

    DFC-328: 0.063 in. (1.6mm)
     
    DCZ-328: 0.059-0.075 in. (1.5-1.9mm)
     
    DCP-306: 0.059-0.075 in. (1.5-1.9mm)
     

  6.  
  7. If not within specification, adjust by bending the pawl at the tip of the lever.
  8.  

Float and Fuel Level

See Figures 5, 6, 7 and 8

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Fig. Fig. 5: Float and fuel level adjustment-1.2L carbureted engine



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Fig. Fig. 6: Float components



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Fig. Fig. 7: Float and fuel level adjustment-1.6L carbureted engine



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Fig. Fig. 8: Float and fuel level adjustment-1.8L carbureted engine

The float level may be adjusted with the carburetor installed on the engine, by removing the air horn as follows:

  1. Disconnect the accelerator pump actuating rod from the pump lever.
  2.  
  3. Remove the throttle return spring.
  4.  
  5. Disconnect the choke cable from the choke lever, and remove it from the spring hanger.
  6.  
  7. Remove the spring hanger, the choke bellcrank and the remaining air horn retaining screws.
  8.  
  9. Lift the air horn slightly, disconnect the choke connecting rod, and remove the air horn.
  10.  
  11. Invert the air horn (float up), and measure the distance between the surface of the air horn and the float.
  12.  
  13. Clearance should be as follows:

    DFC-328: 0.437 in. (11.1mm)
     
    DCZ-328: 0.435-0.492 in. (11.5-12.5mm)
     
    DCP-306: 0.393 in. (10mm)
     

  14.  
  15. If not within specification, bend the float arm until the clearance is correct.
  16.  
  17. Invert the air horn to its installed position.
  18.  
  19. On the DCZ-328 and DCP-306 carburetors, measure the distance between the float arm and the needle valve seat. On the DFC-328 carburetor, measure the distance between the choke chamber and the bottom of the float.
  20.  
  21. Clearance should be as follows:

    DCF-328: 1.835 in. (46.6mm)
     
    DCZ-328: 0.059-0.075 in. (1.5-1.9mm)
     
    DCP-306: 0.051-0.067 in. (1.3-1.7mm)
     

  22.  
  23. If not within specification, adjust by bending the float stops.
  24.  

Primary/Secondary Throttle Linkage

See Figures 9 and 10

Click image to see an enlarged view

Fig. Fig. 9: Measuring throttle valve opening-1.2L carbureted engine



Click image to see an enlarged view

Fig. Fig. 10: Measuring throttle valve opening-1.6L and 1.8L carbureted engines

  1. With the carburetor removed from the engine, operate the linkage so that the connecting rod contacts the groove on the end of the secondary actuating lever.
  2.  
  3. Measure the clearance between the lower end of the primary throttle valve and its bore.
  4.  
  5. Clearance should be as follows:

    DFC-328: 0.236 in. (6.0mm)
     
    DCZ-328: 0.271-0.275 in. (6.89-6.99mm)
     
    DCP-306: 0.236 in. (6.0mm)
     

  6.  
  7. If not within specification, adjust the clearance by bending the connecting rod.
  8.  
  9. Check to make sure that the linkage operates smoothly after performing the adjustment.
  10.  

REMOVAL & INSTALLATION



1.2L Engine

See Figure 11

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Fig. Fig. 11: Exploded view of carburetor assembly-1.2L carbureted engine

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Tag and disconnect the throttle linkage from the carburetor.
  6.  
  7. Tag, disconnect and plug the fuel and vent lines from the carburetor.
  8.  
  9. Tag and disconnect the vacuum lines from the carburetor.
  10.  
  11. Disconnect any electrical harnesses from the carburetor.
  12.  
  13. Remove the four carburetor mounting nuts.
  14.  
  15. Remove the carburetor and gasket from the intake manifold.
  16.  
  17. Clean all gasket surfaces completely.
  18.  

To install:
  1. Install the carburetor using a new base gasket.
  2.  
  3. Install the four carburetor mounting nuts and tighten snugly.
  4.  
  5. Connect the electrical harnesses removed during disassembly.
  6.  
  7. Install the vacuum lines.
  8.  
  9. Connect the fuel and vent lines to the carburetor.
  10.  
  11. Connect the throttle linkage.
  12.  
  13. Install the air cleaner assembly.
  14.  
  15. Connect the negative battery cable.
  16.  
  17. Start the vehicle and verify that there are no fuel leaks.
  18.  

1.6L and 1.8L Engines

See Figures 12 and 13

Click image to see an enlarged view

Fig. Fig. 12: Exploded view of carburetor assembly-1.6L engine



Click image to see an enlarged view

Fig. Fig. 13: Exploded view of carburetor assembly-1.8L engine

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Tag and disconnect the throttle linkage from the carburetor.
  6.  
  7. Tag, disconnect and plug the fuel and vent lines from the carburetor.
  8.  
  9. Tag and disconnect the vacuum lines from the carburetor.
  10.  
  11. Disconnect any electrical harnesses from the carburetor.
  12.  
  13. Disconnect the main diaphragm, distributor advancer, EGR and canister vacuum hoses.
  14.  
  15. Disconnect hoses for the duty solenoid valves (California and 49 state 2WD models).
  16.  
  17. Disconnect FCV and secondary main air bleed hoses (High altitude configuration only).
  18.  
  19. Drain the coolant so as to prevent it from flowing out.
  20.  


CAUTION
When draining the 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 four carburetor mounting nuts.
  2.  
  3. Remove the carburetor and gasket from the intake manifold.
  4.  
  5. Clean all gasket surfaces completely.
  6.  

To install:
  1. Install the carburetor using a new base gasket.
  2.  
  3. Install the four carburetor mounting nuts, and tighten them snugly.
  4.  
  5. Connect the electrical harnesses removed during disassembly.
  6.  
  7. Install the vacuum lines.
  8.  
  9. Connect the Float Control Valve (FCV) and secondary main air bleed hoses (if so equipped).
  10.  
  11. Connect the hoses to the duty solenoid.
  12.  
  13. Connect the main diaphragm, distributor advancer, EGR and canister vacuum hoses.
  14.  
  15. Connect the fuel and vent lines to the carburetor.
  16.  
  17. Connect the throttle linkage.
  18.  
  19. Install the air cleaner assembly.
  20.  
  21. Connect the negative battery cable.
  22.  
  23. Start the vehicle and verify that there are no fuel leaks.
  24.  

OVERHAUL



See Figures 11, 12 and 13

Generally, when a carburetor requires major service, a rebuilt one is purchased on an exchange basis, or a kit may be bought for overhauling the carburetor.

The kit contains the necessary parts and some form of instructions for carburetor rebuilding. The instructions may be as simple as an exploded view, or as detailed as step-by-step rebuilding instructions. Unless you are familiar with carburetor overhaul, it is best to purchase a rebuilt carburetor.

There are some general overhaul procedures which should always be observed:



Efficient carburetion depends greatly on careful cleaning and inspection during overhaul since dirt, gum, water, or varnish in or on the carburetor parts is often responsible for poor performance.
 
Overhaul your carburetor in a clean, dust-free area. Carefully disassemble the carburetor, referring often to the exploded views. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.
 
When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, pump plunger, and any other plastic, leather, fiber, or rubber parts) in clean carburetor solvent. Do not leave parts in the solvent any longer than is necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry. Wipe clean all cork, plastic, leather, and fiber parts with a clean, lint-free cloth.
 
Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages, or air bleeds. Clean all jets and valves separately to avoid accidental interchange.
 
Check all parts for wear or damage. If wear or damage is found, replace the defective parts.
 

Disassembly
  1. Remove the carburetor from the vehicle and place on a clean, suitable workstand.
  2.  
  3. Remove the throttle return spring.
  4.  
  5. Remove the pump lever shaft screw, pump lever, washer and spring washer.
  6.  
  7. Separate the accelerating pump connecting rod and pump lever.
  8.  

Leave the pump connecting rod as it is.

  1. Remove the cam connecting rod, cotter pin and washer.
  2.  
  3. Disconnect the vacuum hose from the main vacuum diaphragm.
  4.  
  5. Detach the choke chamber and gasket from the float chamber.
  6.  

Take care not to damage the duty solenoid valve or float.

  1. Remove the piston return spring, ball and injector weight from the choke chamber.
  2.  
  3. Remove the anti-dieseling switch with plunger and spring.
  4.  
  5. Remove the cotter pin of the secondary diaphragm.
  6.  
  7. Disconnect the secondary diaphragm rod from the secondary throttle valve shaft.
  8.  
  9. Separate the float chamber and throttle chamber. Remove the gasket.
  10.  
  11. Remove the accelerating pump piston and pump cover.
  12.  
  13. Remove the float shaft and float with needle valve.
  14.  
  15. Pull out the duty solenoid valve lead wires from the connector. Remove the rear holder from the housing. Pry up the pawls of the housing and remove the terminal.
  16.  
  17. Remove the primary and secondary slow air bleed.
  18.  
  19. Remove the switch vent solenoid valve and O-ring.
  20.  
  21. Remove the primary and secondary main air bleeds.
  22.  
  23. Remove the primary plug, primary and secondary slow jets.
  24.  
  25. Remove the lockplate, float chamber drain plugs, and primary and secondary main jets.
  26.  
  27. Remove the idle adjusting screw and spring. The idle screw can be removed after turning its protector. If it is hard to remove, drill a hole in the plug.
  28.  
  29. Remove the nut and parts on the throttle valve shaft.
  30.  

Keep all parts in disassembled order. Take care not to damage the throttle shaft and throttle valve.

  1. Remove the throttle adjusting screw and spring.
  2.  

Inspection
  1. Check the float needle and seat for wear. If wear is found, replace the complete assembly.
  2.  
  3. Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
  4.  
  5. Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft, or shaft bore will often require replacement of the throttle body. These parts require a close tolerance. Wear may allow air leakage, which could affect starting and idling.
  6.  

Throttle shafts and bushings are usually not included in overhaul kits. They can be purchased separately.

  1. Inspect the idle mixture adjusting needles for burrs or grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
  2.  
  3. Test the accelerator pump check valves. They should pass air one way but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve if necessary. If the valve is satisfactory, clean the valve with solvent and dry with compressed to remove any moisture.
  4.  
  5. Check the bowl cover for warped surfaces with a straightedge.
  6.  
  7. Closely inspect the valves and seats for wear and damage, replacing as necessary.
  8.  
  9. After the carburetor is assembled, check the choke valve for freedom of operation.
  10.  

Assembly
  1. Attach the switch vent solenoid valve with O-rings.
  2.  
  3. Install the primary and secondary slow air bleeds.
  4.  
  5. Connect the duty solenoid valve.
  6.  

Apply silicone grease to the O-ring of the duty solenoid valve.

  1. Install the needle valve case washer.
  2.  
  3. Attach the float with needle valve and float shaft, and adjust the float level.
  4.  
  5. Position the accelerating pump piston and pump cover.
  6.  
  7. Attach the primary and secondary main jets and float chamber drain plugs with washers and install the lock plate.
  8.  
  9. Position the primary slow jet and then install the plug.
  10.  
  11. Install the secondary slow jet and then connect the air bleed.
  12.  
  13. Install the primary and secondary main air bleeds.
  14.  
  15. Secure the throttle adjusting screw and spring.
  16.  
  17. Install the adjusting plate, lever, washer, sleeve, etc. onto the throttle valve shaft.
  18.  
  19. Put the flat chamber and throttle chamber together with new gaskets.
  20.  

Be sure to attach the throttle valve shaft spring to the float chamber body. After installation, check that both the primary and secondary throttle valve move properly.

  1. Install the idle adjusting screw, spring and screw case. Do not attach the plug at this time.
  2.  
  3. Connect the secondary diaphragm rod to the secondary throttle valve shaft.
  4.  
  5. Position the injector weight. Install the ball and piston return spring.
  6.  

Install the return spring with its hook portion facing downward.

  1. Install the anti-dieseling switch with plunger, spring and washer.
  2.  
  3. Position the throttle chamber on the float chamber with gasket and clamps.
  4.  
  5. Attach the cam connecting rod with cotter pins and plain washers.
  6.  
  7. Connect the accelerating pump connecting rod to the pump lever by inserting the rod end into the hole in the pump lever.
  8.  
  9. Install the pump lever with the pump lever shaft screw, plain washer and spring washer.
  10.  
  11. Connect the idle-up actuator.
  12.  

When installing the idle-up actuator, securely tighten the idle adjusting screw so that the throttle valve does not gouge the throttle bore surface.

  1. Attach the throttle return spring.
  2.  
  3. Connect the vacuum hose to the main vacuum diaphragm.
  4.  
  5. Make sure that all linkages operate smoothly and all lead wires are routed properly.
  6.  
  7. Install the carburetor and adjust the idle speed and idle mixture.
  8.  

 
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