Nissan Z - ZX 1970-1988 Repair Guide

Carburetors

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See Figure 1



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Fig. Fig. 1: Carburetor components and engine plumbing-1970-74 models


CAUTION
Never smoke when working around gasoline! Avoid all sources of sparks or ignition. Gasoline vapors are EXTREMELY volatile!

ADJUSTMENTS



Float Level

See Figure 2



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Fig. Fig. 2: Use a mirror to check the float level

1970-72 MODELS

See Figure 3

  1. Remove the four float chamber cover screws and the cover.
  2.  
  3. Place the cover on a flat surface with the float upward.
  4.  
  5. Lift the float up until the needle valve is open and then lower it just until the needle valve contacts the seat.
  6.  
  7. Measure the distance between fuel level and the top of the float chamber. It should be 0.5-0.6 in. (14-15mm).
  8.  
  9. If necessary, correct the dimension by bending the float lever.
  10.  



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Fig. Fig. 3: Float level adjustment-1970-72 models

  1. Replace the float chamber cover.
  2.  

1973 MODELS

See Figure 4

  1. Remove the carburetor from the engine. Remove the float chamber cover.
  2.  
  3. Measure the distance between the portion of the float lever which contacts the needle valve and the float chamber cover. It should be 0.6 in. (15mm).
  4.  



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Fig. Fig. 4: Measure the distance between the float chamber cover and the float needle valve

  1. If necessary, bend the float lever to adjust the dimension. Recheck to make sure that the dimension is to specification.
  2.  
  3. Install the float chamber cover and reinstall the carburetor on the engine.
  4.  
  5. Check float level by operating the engine and checking that the fuel level is in the center of the float level window.
  6.  

1974 MODELS

See Figures 5 and 6

  1. Remove the carburetor from the intake manifold. Remove the seven attaching screws and remove the float chamber cover.
  2.  
  3. Turn the carburetor upside down to check the position of the float lever. Both floats should touch the inner wall of the carburetor.
  4.  



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Fig. Fig. 5: Measure distance H



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Fig. Fig. 6: Measure distance G

  1. Measure dimension "H'' between the end face of the float chamber and the float lever tongue which contacts the needle valve (point "A''). It should be 0.4-0.5 in. (12-13mm).
  2.  
  3. If necessary, bend the float lever near the float to bring the dimension to within specifications.
  4.  
  5. Turn the carburetor right side up. Measure the gap "G'' between the power valve nozzle and float. It should be 0.02-0.08 in. (0.5-2.0mm).
  6.  
  7. Adjust the gap, as necessary, by bending the stop as required; then, recheck dimension "H.''
  8.  
  9. Install the float chamber cover and install the carburetor on the engine.
  10.  
  11. When the engine is operating, the fuel level should be even with the center line of the float level window.
  12.  

Fast Idle
1970-72 MODELS

See Figure 7

  1. Measure the clearance between the throttle valve and bore when the choke lever is out all the way. The clearance should be 0.023-0.27 in. (0.59-0.69mm).
  2.  



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Fig. Fig. 7: Adjustment of the fast idle opening-1970-72 models

  1. Correct the clearance by bending the connecting rod.
  2.  

Making the rod longer increases the clearance.

1973-74 MODELS

See Figures 8 and 9

  1. Place the fast idle screw on the first step of the fast idle cam.
  2.  



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Fig. Fig. 8: Fast idle opening adjustment-1973 models



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Fig. Fig. 9: Fast idle opening adjustment-1974 models

  1. Adjust the screw so that the clearance between the throttle valve and the lower throttle bore is 0.023-0.024 in. (0.59-0.64mm).
  2.  

Choke Valve

1974 MODELS

See Figure 10

  1. Close the choke valve all the way.
  2.  
  3. Hold the valve shut by stretching a rubber band between the lever connected to the choke wire and the carburetor.
  4.  



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Fig. Fig. 10: Choke valve (plate) adjustment

  1. Using a pair of pliers, gently grip the diaphragm rod and pull it all the way out.
  2.  
  3. Hold the rod in this position, then check the gap between the choke valve and carburetor body. The gap should be 0.09 in. (2.35mm).
  4.  
  5. Bend the choke piston rod as necessary to secure the proper adjustment.
  6.  

Suction Piston and Chamber
  1. Remove the air cleaner and the oil cap nut.
  2.  
  3. Gradually raise the suction piston with a suitable probe on 1973-74 models. On 1970-72 carburetors, the piston should be raised so that the lifter is well beyond the point where the lifter head contacts the suction piston.
  4.  
  5. Release the piston. The piston should drop smoothly and a sucking sound should be audible.
  6.  
  7. Install the oil cap nut. Raise the suction with your finger, going in through the throttle bore and then let it drop. The piston should resist rising due to damper operation and it should return to the bottom of its travel smoothly. Otherwise, the piston and chamber require cleaning.
  8.  

REMOVAL & INSTALLATION



The 1970-74 models are the only carburetor-equipped vehicles covered by this guide.

  1. Remove the three thumb screws and detach the air cleaner cover.
  2.  
  3. Disconnect all of the hoses between the air cleaner and other components.
  4.  
  5. Remove the six screws retaining the air cleaner flange to the carburetors and remove the air cleaner.
  6.  
  7. Remove the fuel and hoses from the carburetors. Remove the bypass hose from the front carburetor.
  8.  
  9. Remove the distributor and the canister vacuum hose from the front carburetor.
  10.  
  11. Remove the EGR vacuum hose from the rear carburetor (1970-73 models).
  12.  
  13. Remove the coolant inlet hose from the front carburetor and the outlet hose from the rear carburetor.
  14.  
  15. Disconnect the throttle linkage and (on earlier models) the choke linkage.
  16.  
  17. Remove the mounting nuts and the carburetors.
  18.  
  19. To separate the two carburetors, disconnect, then remove the air bypass and coolant hoses.
  20.  
  21. To install, reverse the removal procedures.
  22.  

OVERHAUL



1970-72 Models

To disassemble the carburetors:

  1. Remove the screws and suction chamber.
  2.  
  3. Remove the suction spring, nylon packing and suction piston from chamber. Be extremely careful not to bend the jet needle.
  4.  
  5. DO NOT remove the jet needle from the suction piston unless it must be replaced. To remove, loosen the jet needle setscrew. Hold the needle with pliers at a point no more than 0.98 in. (2.5mm) from the piston. Remove the needle by pulling and turning it slowly. Replace the needle with the shoulder portion flush with the piston surface. Check this with a straightedge. Tighten the setscrew.
  6.  
  7. Clean the parts of the suction chamber assembly with a safe solvent. Reassemble, using all new parts supplied in the overhaul kit. DO NOT lubricate the piston.
  8.  
  9. To dismantle the nozzle assembly, remove the 4mm screw and the connecting plate from nozzle head by pulling lightly on the starter (choke) lever. Remove the fuel line and the nozzle. Be careful not to bend the jet needle if the suction chamber assembly is mounted on the carburetor. Remove the idle (mixture) adjusting nut and spring. DO NOT remove the nozzle sleeve unless absolutely necessary. Special care is required to replace this part. Remove the nozzle sleeve setscrew and the nozzle sleeve.
  10.  
  11. Clean the parts of nozzle assembly with a safe solvent. Be very careful of the nozzle. DO NOT pass anything through the nozzle for cleaning purposes.
  12.  
  13. The jet needle must now be carefully centered in the nozzle, unless the nozzle sleeve and setscrew were not disturbed. Even so, it is a good idea to check this. To center the jet needle, perform the following procedures:
    1. Insert the nozzle sleeve into the carburetor body with the setscrew loose.
    2.  
    3. Carefully install the suction piston assembly without the plunger rod.
    4.  
    5. Insert the nozzle without the spring and mixture adjusting nut until the nozzle contacts the nozzle sleeve.
    6.  
    7. Position the nozzle sleeve so that the jet needle is centered inside the sleeve and does not contact the sleeve.
    8.  
    9. Test the centering by raising and releasing the suction piston. It should drop smoothly, making a metallic sound when it hits the stop.
    10.  
    11. Tighten the nozzle sleeve setscrew when the needle is centered.
    12.  

  14.  
  15. Reassemble the nozzle assembly. Install the fuel line and the damper plunger rod.
  16.  
  17. Pull the starter lever slightly, then replace the connecting plate and the 4mm screw.
  18.  
  19. Carburetor synchronization and mixture adjustments MUST BE performed after reinstalling the carburetors. Refer to the idle adjustment procedure in Engine Performance and Tune-up .
  20.  

1973-74 Models

On 1973-74 models, the factory does not recommend overhaul, except as described below, because of the extreme precision with which carburetors are calibrated at the factory.

FLOAT CHAMBER
  1. Loosen the mounting screws and remove the float chamber cover.
  2.  
  3. On 1973 models only, remove the clip and the needle valve parts. DO NOT touch the needle jet setting nut or bend the float stopper.
  4.  
  5. Reassemble the needle valve parts.
  6.  
  7. Adjust the float level as earlier in this section.
  8.  
  9. Install the float chamber cover.
  10.  

Do not attempt to remove the float and needle valve parts on 1974 models.

POWER VALVE

If the carbon monoxide (CO) emissions in the exhaust are abnormally high and there is no obvious reason, check the power valve. Remove the mounting screws and the valve from the carburetor. Remove the other screws and disassemble the valve. Carefully inspect the diaphragm and replace it, if necessary. Reassemble and install the valve.

 
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