GM Prizm/Nova 1985-1993 Repair Guide

Carburetor - Part Two

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REMOVAL & INSTALLATION



See Figure 1

Each fuel and vacuum line must be tagged or labeled individually during disassembly.



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Fig. Fig. 1: Tag and label every hose during disassembly

  1. Remove the air cleaner assembly.
  2.  
  3. Disconnect the accelerator cable from the carburetor.
  4.  
  5. If equipped with automatic transmission, disconnect the throttle position cable.
  6.  
  7. Unplug the wiring connector.
  8.  
  9. Label and disconnect the:
    1. carburetor vacuum hoses
    2.  
    3. fuel inlet hoses
    4.  
    5. charcoal canister hose
    6.  

  10.  


CAUTION
The carburetor contains gasoline. Wear eye protection and contain spillage. Observe no smoking/no open flame precautions. Have a Class B-C (dry powder) fire extinguisher within arm's reach at all times.

  1. Remove the carburetor mounting nuts.
  2.  
  3. Remove the cold mixture heater wire clamp and lift out the EGR vacuum modulator bracket.
  4.  
  5. Lift the carburetor off the engine and place it on a clean cloth on the workbench. If desired, the insulator (base gasket) may also be removed.
  6.  
  7. Cover the inlet area of the manifold with clean rags. This will prevent the entry of dust, dirt and loose parts.
  8.  

To install:
  1. Place the insulator on the manifold, making sure it is correctly positioned.
  2.  
  3. Install the carburetor onto the manifold.
  4.  
  5. Install the EGR vacuum modulator bracket. Clamp the cold mixture heater wire into place.
  6.  
  7. Tighten the carburetor mounting nuts.
  8.  
  9. Reconnect the fuel inlet hose, the charcoal canister hose and the vacuum hoses.
  10.  
  11. Connect the wiring connector.
  12.  
  13. Connect the accelerator cable; connect the throttle position cable if equipped with automatic transmission.
  14.  
  15. Reinstall the air cleaner.
  16.  

CARBURETOR OVERHAUL



See Figures 2 through 23

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 necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and check 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, and fiber parts with 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. Pay special attention to the following areas:

  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 the replacement of the throttle body. These parts require a close tolerance of fit; wear may allow air leakage, which could affect starting and idling.
  6.  

Throttle shafts and bushings are not included in overhaul kits. They may be available 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 1 way but not the other. 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 (plate) for freedom of operation.
  10.  

Carburetor overhaul kits are recommended for each overhaul. These kits contain all the 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.

Some carburetor manufacturers supply overhaul kits of 3 basic types: minor repair; major repair; and gasket kits. Generally, they contain the following:

Minor Repair


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

Major Repair Kits:


All jets and gaskets
 
All diaphragms
 
Float needle valve
 
Volume control screw
 
Pump ball valve
 
Float(s)
 
All gaskets
 

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 the needle valve(s) into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level when reassembling.



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Fig. Fig. 2: Nova carburetor, exploded detail



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Fig. Fig. 3: Exploded view of the Nova carburetor

The following instructions are organized so that only 1 component group is being worked on at a time. This helps avoid confusion and interchange of parts. To make reassembly easier, always arrange disassembled parts in order on the workbench. Be very careful not to mix up or lose small pieces such as balls, clips or springs.Reassembly and adjustment of the carburetor requires accurate measuring equipment capable of checking clearances to the1/10mm. These specialized carburetor clearance gauges are available at reputable tool retailers but may be difficult to find.

  1. Remove the carburetor as outlined previously.
  2.  
  3. To remove the AIR HORN assembly, disconnect the choke link and the pump connecting rod.
  4.  
  5. Remove the pump arm pivot screw and the pump arm.
  6.  
  7. Remove the fuel hose and union.
  8.  
  9. Remove the 8 air horn screws. Be careful to identify and collect the external parts attached to the screws, such as wire clamps, brackets and the steel number plate.
  10.  
  11. Disconnect the choke link.
  12.  
  13. Lift the air horn with its gasket from the body of the carburetor.
  14.  
  15. Disconnect the wires at the connector.
  16.  
  17. Remove the first and second solenoids from the carburetor body.
  18.  
  19. Remove the float pivot pin, float and needle valve assembly.
  20.  
  21. Remove the air horn gasket.
  22.  
  23. Remove the needle valve seat and gasket.
  24.  
  25. Remove the power piston retainer, power piston and spring.
  26.  
  27. Pull out the pump plunger and remove the boot.
  28.  



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Fig. Fig. 4: Carburetor pump linkage



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Fig. Fig. 5: Needle valve removal



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Fig. Fig. 6: Removing the power piston



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Fig. Fig. 7: Float and needle valve components

  1. Begin disassembly of the BODY by removing the throttle positioner. Disconnect the link and remove the 2 bolts.
  2.  
  3. Remove the stopper gasket, the pump discharge weight, the long spring and the large discharge ball.
  4.  
  5. Using a pair of tweezers, remove the plunger retainer and the small ball.
  6.  
  7. Remove the slow jet from the body.
  8.  
  9. Remove the power valve with the jet.
  10.  
  11. Disassemble the power valve and jet.
  12.  
  13. Remove the throttle positioner levers. Remove the primary main passage plug, primary main jet and the gasket.
  14.  
  15. Remove the auxiliary accelerator pump (AAP) housing, spring and diaphragm.
  16.  
  17. Remove the inlet plug and the small ball for the AAP.
  18.  
  19. Remove the outlet plug, short spring and the small ball.
  20.  
  21. Remove the primary and secondary venturies.
  22.  



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Fig. Fig. 8: Accelerator pump check balls and components



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Fig. Fig. 9: Removing the power valve



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Fig. Fig. 10: Removing the main jets

  1. Remove the sight glass retainer, the glass and its O-ring.
  2.  



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Fig. Fig. 11: Removing the auxiliary accelerator pump



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Fig. Fig. 12: Removing the auxiliary accelerator pump check ball plugs



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Fig. Fig. 13: Body and linkage retaining screws. Note that one screw contains a vacuum passage

  1. Remove the throttle return spring and the throttle back spring.
  2.  
  3. Remove the nut and the throttle lever.
  4.  
  5. Remove the bolt and the fast idle cam.
  6.  
  7. Remove the secondary throttle valve diaphragm by disconnecting the linkage and removing the assembly with its gasket.
  8.  
  9. Remove the 3 bolts and the vacuum passage bolt. Separate the carburetor body from the carburetor flange.
  10.  



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Fig. Fig. 14: Inspecting the power piston

  1. Clean all the disassembled parts before inspecting them. Wash and clean the cast metal parts with a soft brush in carburetor cleaner. Clean off the carbon around the throttle plates. Wash the other parts thoroughly in cleaner. Blow all dirt and other foreign matter from the jets, fuel passages and restrictions within the body.
  2.  
  3. Inspect the float and needle valve. Check the pivot pin for scratches and excessive wear. Inspect the float for breaks in the lip and wear in the pivot pin holes. Check the needle valve plunger for wear or damage and the spring for deformation. The strainer should be checked for rust or breaks.
  4.  
  5. Make certain the power piston moves smoothly within its bore.
  6.  
  7. Check the power valve for proper air flow. In its normal (expanded) condition, no air should pass through it. When compressed at 1 end, air should enter the end and exit through the side vent.
  8.  
  9. Inspect the fuel cut solenoids. Connect the solenoid leads to the battery terminals (the solenoid with only 1 lead requires a jumper between the case and the battery) and check that the solenoid clicks as the last connection is made. The solenoid should click each time the battery is connected or disconnected. If a solenoid is not operating correctly, replace it.
  10.  
  11. Install new O-rings on the solenoids.
  12.  
  13. Inspect the choke heater by using an ohmmeter to measure its resistance. Correct resistance is 18 ohms. If a problem is found, the air horn assembly must be replaced.
  14.  



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Fig. Fig. 15: Testing the primary (left) and secondary fuel cut solenoids



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Fig. Fig. 16: Checking the resistance of the choke heater

  1. Reassembly begins by placing a new gasket and the carburetor body onto the flange.
  2.  
  3. Install the vacuum passage bolt, then install the 3 retaining bolts.
  4.  
  5. Assemble the secondary throttle diaphragm, position the gasket and install the assembly. Connect the linkage.
  6.  



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Fig. Fig. 17: Installing the secondary throttle valve diaphragm

  1. Install the fast idle cam with the bolt.
  2.  
  3. Install the throttle lever with its nut.
  4.  
  5. Install the throttle back spring and the throttle return spring.
  6.  
  7. Install the sight glass with its O-ring and retainer.
  8.  
  9. Install the primary and secondary small venturies over new gaskets. Install the O-ring on the primary small venturies.
  10.  
  11. Install the auxiliary accelerator pump by first installing the outer plug, the short spring and the small ball. Install the inlet plug and the small ball, followed by the AAP housing, spring and diaphragm.
  12.  
  13. Install the primary main jet and passage plug with a new gasket.
  14.  
  15. Install the secondary main jet and passage plug with a new gasket.
  16.  
  17. Install the throttle lever.
  18.  
  19. Install the slow jet.
  20.  
  21. Assemble the power valve and jet and install them in position.
  22.  
  23. Install the discharge large ball, the long spring, the pump discharge weight and the stopper gasket.
  24.  
  25. Use tweezers to insert the plunger small ball and the retainer.
  26.  
  27. Reinstall the throttle positioner and connect its linkage.
  28.  
  29. On the air horn, install the valve seat over the gasket into the fuel inlet.
  30.  
  31. Install the needle valve, spring, and plunger onto the seat.
  32.  
  33. Install the float and pivot pin.
  34.  
  35. Measure and adjust the float clearances (level) by following procedures and specifications outlined earlier in this chapter.
  36.  
  37. After adjusting the float level, remove the float, plunger, spring and needle valve. Assemble the pin clip onto the needle valve.
  38.  



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Fig. Fig. 18: Install the pin clip after the float is adjusted

  1. Install the power piston spring and piston into its bore and install the retainer.
  2.  
  3. Install the acceleration pump plunger and its boot.
  4.  
  5. Place a new gasket onto the air horn.
  6.  
  7. Install the needle valve assembly, the float and the pivot pin. Insert the float lip between the plunger and the clip when installing the float.
  8.  
  9. Install the solenoid valves into the body of the carburetor.
  10.  
  11. Assemble the air horn and body. Install the 8 screws, paying particular attention to the various brackets, wire clamps and steel number plate.
  12.  
  13. Install the accelerator pump arm. Install the pump arm to the air horn with the pump plunger hole and lever aligned.
  14.  
  15. Connect the choke link and the pump connecting link.
  16.  
  17. Install the fuel pipe and union.
  18.  
  19. With the carburetor still on the bench, move the various linkages by hand, checking for smooth operation.
  20.  
  21. Check the throttle plate for full opening. It should move 90° from horizontal. If needed, adjust its travel by bending the first throttle lever stopper.
  22.  
  23. Check the clearance of the secondary throttle plate. When wide open, the secondary throttle plate should have 13mm clearance to the body of the bore. Adjust this clearance by bending the secondary throttle lever stopper.
  24.  
  25. Check the clearance for the secondary touch. This is the point at which the secondary throttle begins to open under acceleration. Move the primary throttle plate open, watching for the point at which the first kick lever just touches the second kick lever. At this point, the primary throttle plate should have 0.230 in. clearance.
  26.  



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Fig. Fig. 19: Adjusting the primary throttle plate



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Fig. Fig. 20: Adjusting the secondary throttle plate clearance



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Fig. Fig. 21: Measuring and adjusting the secondary touch

  1. Set the throttle lever to the first step of the fast idle cam. With the choke plate fully closed, check the clearance of the primary throttle plate. The correct clearance is 1.15mm; the clearance may be adjusted by turning the fast idle adjusting screw.
  2.  
  3. The choke unloader is adjusted by bending the fast idle lever as necessary. Open the primary throttle plate fully (with the choke plate closed, from the previous Step) and check that the choke plate has 3mm of clearance.
  4.  
  5. Check the choke breaker. Hold the throttle slightly open, push the choke closed and hold it closed as your release the throttle. Apply vacuum to the choke breaker 1st diaphragm. The choke plate should have 2.5mm of clearance. The clearance is adjusted by bending the relief lever.
  6.  
  7. Now apply vacuum to both the first and second diaphragms. Clearance at the choke plate should become 6mm. Adjustment is by turning the diaphragm adjustment screw.
  8.  



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Fig. Fig. 22: Adjusting the fast idle setting



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Fig. Fig. 23: Adjusting the choke unloader

  1. Release the choke and throttle settings. With the choke plate fully open, measure the length of the pump stroke. Correct stroke is 2mm; it may be adjusted by bending the connecting link.
  2.  
  3. Reinstall the carburetor on the intake manifold, following directions outlined earlier.
  4.  
  5. Start the engine and allow it to warm up normally. During this time, pay careful attention to the high idle speed, the operation of the choke and its controls and the idle quality. If you worked carefully and accurately, and performed the bench set-up properly, the carburetor should need very little fussing after it's reinstalled.
  6.  

 
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