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    Subaru ff-1/1300/1400/1600/1800/Brat 1970-1984 Repair Guide

    Carburetor

    Print

    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 the 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.

    All carburetors except the C-W are 2-barrel, down-draft carburetors which supplies the best air/fuel mixture under any operating condition. The C-W is a 1-barrel carburetor.

    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 by-pass system which helps control exhaust emissions during deceleration.

    A hand control (manual) choke was used on Subaru models until 1973. From 1974 until present an automatic control choke is used. The automatic choke and a throttle chamber heated by engine coolant, to prevent throttle bore icing, help the Subaru start and run well in the coldest conditions.

    The basic systems of the carburetor are:

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

    5. Secondary side
    6.  
      1. Step system
      2.  
      3. Main system
      4.  

    7. Coasting by-pass system.
    8.  

    On the following pages illustrations will help you better understand the systems and what functions they perform.

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

    ADJUSTMENTS



    Fast Idle
    1970-73 MODELS
    1. With the carburetor removed from the engine, make sure that the choke valve is fully closed.
    2.  
    3. Measure the clearance between the upper edge of the primary throttle valve and its bore with a wire gauge. It should be the appropriate figure given in the chart at the end of this Section.
    4.  
    5. If the clearance is incorrect, adjust it by bending the choke adjusting rod.
    6.  
    7. Check the operation of the linkage for smoothness after adjustment is completed.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 1 Fast idle adjustment-1970-73 models



    Click image to see an enlarged view

    Fig. Fig. 2 Fast idle adjustment from 1974-except C-W



    Click image to see an enlarged view

    Fig. Fig. 3 Fast idle adjustment specifications

    1974 AND LATER MODELS (EXCEPT C-W)
    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 its bore. The clearance should be the value specified in the Fast Idle chart in this section.
    6.  
    7. If the clearance is incorrect, turn the fast idle adjusting screw to bring it within specifications. Turning the screw in increases the throttle clearance and vice-versa.
    8.  

    Float and Fuel Level
    ALL MODELS

    Float level adjustments are unnecessary, on models equipped with a sight glass on the carburetor float bowl, if the fuel is level within 0.05 in. (1.5mm) with the dot on its center, when the engine is running.

    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. Bend the float arm until the clearance is approximately 10mm.
    14.  
    15. Invert the air horn to its installed position, and measure the distance between the float arm and the needle valve stem. This dimension should be 0.05-0.06 in. (1.3-1.7mm), and is adjusted by bending the float stops.
    16.  



    Click image to see an enlarged view

    Fig. Fig. 4 Float level adjustment

    Primary/Secondary Throttle Linkage
    ALL MODELS
    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. It should be about 6mm (the size of the shank of a 1 / 4 in. drill bit) for all models.
    4.  
    5. Adjust the clearance by bending the connecting rod.
    6.  
    7. Check to make sure that the linkage operates smoothly after performing the adjustment.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 5 Primary and secondary linkage adjustment

    Manual Choke Cable
    1970-73 MODELS
    1. Pull the choke knob on the instrument panel out all the way. Remove the air cleaner and check the position of the choke valve. If the choke valve is fully closed, the cable is adjusted properly.
    2.  
    3. If the choke valve is not fully closed, adjust the cable by loosening its retaining nut and pulling on the cable lightly to take up any slack.
    4.  
    5. Tighten the retaining nut.
    6.  
    7. Check to see that the choke valve is now fully opened when the choke knob is pushed all the way in.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 6 Main diaphragm and linkage adjustment

    Automatic Choke
    1974 AND LATER (EXCEPT C-W)

    WARNING
    The choke is not adjustable on 1982-84 models

    1. Adjust the fast idle as detailed in this section, and perform the adjustments which follow, in the sequence given.
    2.  
    3. Pull the main choke diaphragm lever as far as it will go to the left and measure the clearance between the upper end of the choke valve and its bore with a wire gauge. The clearance should be 0.04-0.05 in. (1.2-1.4mm). Adjust, as necessary, by bending the diaphragm-to-choke connecting rod.
    4.  
    5. Apply 8-9 in.Hg of vacuum to the main diaphragm, it should operate the choke valve. If it does not, replace the diaphragm with a new one.
    6.  
    7. Place the fast idle cam adjusting lever on the third step of the fast idle cam. Measure the clearance between the upper end of the choke valve and its bore. The clearance should be 0.06-0.07 in. (1.6-1.9mm) for 1974-76 cars; 0.025-0.037 in.(0.66-0.94mm) for cars from 1977. Carefully bend (turn) the fast idle cam to obtain the correct clearance, as necessary. To obtain the clearance, bend the cam clockwise. To decrease it, bend the cam counter clockwise.
    8.  
    9. Loosen the 3 choke cap securing screws, and match the line on it up with the longest line on the choke coil housing. Tighten the retaining screws.
    10.  


    CAUTION
    Do not loosen the screw which secures the choke lever.

    1. Fit the tank on the bi-metal lever, which is connected to the auxiliary diaphragm, against the stop in the choke coil housing. Pull the setting piston of the auxiliary diaphragm back and, with the piston in this position, tighten the compensator adjusting screw so that it contacts the tang on the bi-metal lever. The gap should be 0.1 in. (5mm), on 1974-76 cars and 0.03 in.(0.86mm) on 1977 and later models.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 7 Auxiliary diaphragm must be adjusted during the auto choke adjustment

    1. Apply vacuum from an outside source to the auxiliary diaphragm. It should take 9.5-11.8 in.Hg of vacuum to operate the diaphragm on 1974-76 cars and 6.9-9.2 in.Hg of vacuum in 1977 and later models. To adjust the vacuum setting, bend the diaphragm rod. Vacuum is reduced when the rod is bent to shorten it and increased when the rod is bent to lengthen it.
    2.  


    WARNING
    When the setting piston is released, there should be no clearance between the tan on the bi-metal lever and the stop on the coil housing. If they don't contact, the bi-metal lever has been bent too much.

    REMOVAL & INSTALLATION



    1970-73 Models
    1. Remove the spare tire from the engine compartment.
    2.  
    3. Disconnect the emission control system hoses from the air cleaner case, unfasten the bracket bolts, unscrew the wing nut, and remove the air cleaner assembly from the carburetor.
    4.  
    5. Disconnect the fuel lines from the carburetor. Unfasten the vacuum hoses from the distributor port (ff-1 and 1300G) or the servo diaphragm (DL and GL).
    6.  
    7. On DL and GL models, disconnect the anti-dieseling solenoid wiring.
    8.  
    9. Detach the choke cable from the choke lever and spring hanger, then remove the throttle cable from the throttle lever.
    10.  
    11. Remove the 4 carburetor mounting bolts and lift the carburetor, with gasket, off the intake manifold. Be sure to cover the manifold opening, to prevent anything from being dropped down it.
    12.  
    13. Install the new or rebuilt carburetor and gasket onto the intake manifold.
    14.  
    15. Install the 4 carburetor mounting bolts and tighten them securely.
    16.  


    WARNING
    Do not over-tighten the carburetor bolts. Carburetors are made of soft metal and can be easily cracked.

    1. Install the throttle cable, choke cable and anti-dieseling solenoid wiring onto the carburetor.
    2.  
    3. Connect the vacuum hoses to either the distributor port or servo diaphragm, depending on the model.
    4.  
    5. Connect the fuel lines, install the air cleaner, connect the emission control hoses and replace the spare tire.
    6.  
    7. Be sure to adjust the choke cable, idle speed (see ), and make any other necessary adjustments.
    8.  

    1974-81 Models
    1. Remove the air cleaner emission control system hoses, mounting bracket screws, wing nut or nuts, and lift the air cleaner assembly off the carburetor.
    2.  
    3. Disconnect the fuel lines from the carburetor.
    4.  
    5. Unfasten the vacuum hoses from the servo diaphragm, automatic choke diaphragms, distributor, and the EGR port (if so equipped).
    6.  
    7. Disconnect the anti-dieseling switch and automatic choke heater electrical leads. On California vehicles and some other models disconnect switch vent solenoid valve wire and hose to canister.
    8.  
    9. Remove the accelerator cable from the throttle lever.
    10.  
    11. Unfasten the 4 nuts which secure the carburetor and take it off the intake manifold. Cover the hole in the intake manifold, to prevent anything from falling in.
    12.  
    13. Install the new or rebuilt carburetor and gasket onto the intake manifold.
    14.  
    15. Install the 4 carburetor mounting bolts and tighten them securely.
    16.  


    WARNING
    Do not over-tighten the carburetor bolts. Carburetors are made of soft metal and can be easily cracked.

    1. Install the vacuum hoses from the servo diaphragm, automatic choke diaphragms, distributor, and the EGR port (if so equipped).
    2.  
    3. Connect the anti-dieseling switch and automatic choke heater electrical leads. On California and some other models, connect switch vent solenoid valve wire and hose to the canister.
    4.  
    5. Connect the fuel lines, install the air cleaner, connect the emission control hoses and replace the spare tire.
    6.  
    7. Be sure to adjust the choke cable, idle speed (see ), and make any other necessary adjustments.
    8.  

    1982-84 Models
    1. Remove the air cleaner.
    2.  
    3. Disconnect fuel supply and return lines at the carburetor.
    4.  
    5. Disconnect the carburetor vent hose for the ECC system.
    6.  
    7. Disconnect remaining vacuum hoses to distributor, etc.
    8.  
    9. Disconnect the EGR tube.
    10.  
    11. On the Hitachi carburetor:
    12.  
      1. Disconnect the ignition retard, if applicable.
      2.  
      3. Disconnect vacuum hoses for solenoid valves, the main diaphragm, and, on high altitude carburetors, the secondary main air bleed.
      4.  
      5. Disconnect the duty solenoid valve connector on those models so equipped.
      6.  




    Click image to see an enlarged view

    Fig. Fig. 8 Remove the air cleaner



    Click image to see an enlarged view

    Fig. Fig. 9 Disconnect the hoses from the carburetor

    1. On both types of carburetor, disconnect the harness connectors and then disengage the accelerator cable from the throttle lever.
    2.  
    3. Drain some coolant out of the radiator so as to drain water out of the water heated throttle bore.
    4.  


    CAUTION
    When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to 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 mounting nuts on the Hitachi or two nuts on the C-W, and remove the carburetor. On the C-W, disconnect the vent hose and remove its connector with the spacer and gasket. Cover the intake manifold opening.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 10 Disengage the accelerator cable from the throttle lever



    Click image to see an enlarged view

    Fig. Fig. 11 Remove the carburetor from the intake manifold



    Click image to see an enlarged view

    Fig. Fig. 12 Clean the carburetor mounting surface

    To install:

    1. Clean the carburetor mounting surface.
    2.  
    3. Install the carburetor onto the intake manifold and tighten the mounting bolts.
    4.  
    5. On the C-W, connect the vent hose, spacer and gasket.
    6.  
    7. Engage the accelerator cable to the throttle lever and the harness connector to the carburetor.
    8.  
    9. On the Hitachi carburetor:
    10.  
      1. Connect the duty solenoid valve connector on those models so equipped.
      2.  
      3. Connect vacuum hoses for solenoid valves, the main diaphragm, and, on high altitude carburetors, the secondary main air bleed.
      4.  
      5. Connect the ignition retard, if applicable.
      6.  

    11. Connect the EGR tube.
    12.  
    13. Connect the vacuum hoses to the distributor.
    14.  
    15. Connect the carburetor vent hose for the ECC system.
    16.  
    17. Connect the fuel lines to the carburetor and install the air cleaner.
    18.  
    19. Make any necessary adjustments to the carburetor, check fuel lines for leaks and refill the radiator with coolant.
    20.  

    OVERHAUL NOTES



    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 which varies on the kit type and some form of instructions for carburetor rebuilding. The instructions may vary from a simple exploded view to detailed step-by-step rebuilding instructions. Unless you are familiar with carburetor overhaul, the latter should be used.

    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 are 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. Especially check the following:

    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.  


    WARNING
    Throttle shafts and bushings are usually not included in overhaul kits. They can be usually 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, wash the valve again to remove breath 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.  

    Carburetor overhaul kits are recommended for each overhaul. These kits contain all gaskets and new parts to replace those that deteriorate most rapidly. Failure to replace all parts supplied with the kit (especially gaskets) can result in poor performance later.

    Most carburetor manufacturers supply overhaul kits of three basic types: minor repair, major repair, and gasket kits. Basically, they contain the following:

    Minor Repair Kits:



    All gaskets
     
    Float needle valve
     
    Volume control screw
     
    All diaphragms
     
    Spring for the pump diaphragm
     

    Major Repair Kits:



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

    Gasket Kits:



    All gaskets
     

    After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are tight in their seats, but do not overtighten, as the tips will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats. Uneven jetting will result. Always use new gaskets. Be sure to adjust the float level when reassembling.



    Click image to see an enlarged view

    Fig. Fig. 13 Exploded view ff-1 and 1300G carburetor



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    Fig. Fig. 14 Exploded view 1972-73 GL and DL carburetor



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    Fig. Fig. 15 1974 carburetor (1975-79 differs in jet size only)



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    Fig. Fig. 16 1980 DCP306-1, DCP306-3, DCP306-4 and DCP306-5 carburetors



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    Fig. Fig. 17 Components, 1980 DCP306-1, DCP306-3, DCP306-4 and DCP306-5 carburetors



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    Fig. Fig. 18 DCJ306-15 carburetor used in 1980



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    Fig. Fig. 19 Components, DCJ306-15 carburetor used in 1980



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    Fig. Fig. 20 1983-84 Hitachi carburetor



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    Fig. Fig. 21 Components, 1983-84 Hitachi carburetor



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    Fig. Fig. 22 1983-84 Carter-Weber carburetor



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    Fig. Fig. 23 Components, 1983-84 Carter-Weber carburetor



    Click image to see an enlarged view

    Fig. Fig. 24 Carburetor Jet Specifications Chart

     
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