Isuzu Cars and Trucks 1981-1991

Carbureted Engine Fuel System

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idle speed adjustment
All Engines

NOTE
The idle speed adjusting screw is located on the passenger side of the carburetor at the throttle cable side on G180Z and G200Z engines.

  1. Firmly set the parking brake and block the drive wheels.
  2.  
  3. Place the transmission in N .
  4.  
  5. Operate the engine until it reaches normal operating temperatures. Be sure the choke is fully open and the air cleaner is installed. If equipped, turn the air conditioning OFF .
  6.  
  7. Disconnect and plug the distributor vacuum, the canister purge and EGR vacuum hoses. Shut off the vacuum to the idle compensator by bending the rubber hose.
  8.  
  9. Turn the throttle adjusting screw to the required idle speed.
  10.  
  11. If equipped with air conditioning, turn the air conditioning control to MAX COLD and the blower on HIGH .
  12.  
  13. Open the throttle to approximately 1 / 3 opening and allow it to close.
  14.  


NOTE
The speed-up solenoid should reach full travel.



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Fig. Adjusting screws on the 4XC1-U carburetor

  1. Adjust the speed up solenoid screw to 850 and 19950 rpm.
  2.  

idle mixture adjustment
Except California Engines
  1. Firmly set the parking brake and block the drive wheels.
  2.  
  3. Place the transmission in N
  4.  
  5. Remove the carburetor assembly.
  6.  
  7. Using a drill, drill a hold through the sealing plug covering the idle mixture screw and pry the plug from the carburetor.
  8.  
  9. Reinstall the carburetor.
  10.  
  11. Operate the engine until it reaches normal operating temperatures. Be sure the choke is fully open, and the air cleaner is installed. If equipped, turn the air conditioner OFF .
  12.  
  13. Disconnect the plug the distributor vacuum, the canister purge and EGR vacuum lines. Shut off the vacuum to the idle compensator by bending the rubber hose.
  14.  
  15. Turn the throttle adjusting screw until the engine speed is 800 rpm (manual transmission) or 900 rpm (automatic transmission).
  16.  
  17. Adjust the idle mixture screw to achieve the maximum speed.
  18.  
  19. Reset the throttle adjusting screw until the engine speed reaches the specification in the Tune-Up Chart.
  20.  
  21. Turn the idle mixture screw counterclockwise (lean) until the engine speed is 750 and 19850 rpm (manual transmission) or 850 and 19950 rpm (automatic transmission).
  22.  
  23. Reinstall a mixture adjustment plug.
  24.  



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Fig. Removing the mixture screw plug carbureted engines except 4XC1-U



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Fig. Idle mixture screw concealment plug removal 4XC1-U engine



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Fig. Before checking idle, disconnect the VSV pressure regulator 1983 and 1988 EFI Impulse



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Fig. Before checking idle, disconnect the VSV pressure regulator 1983 and 1999 EFI Impulse



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Fig. Idle speed adjusting screw 1983 and 1988 Impulse with G200Z, 4ZD1 and 4ZC1-T

California Engines
  1. Firmly set the parking brake and block the drive wheels.
  2.  
  3. Place the transmission in N
  4.  
  5. Remove the carburetor assembly.
  6.  
  7. Using a drill, drill a hold through the sealing plug covering the idle mixture screw and pry the plug from the carburetor.
  8.  
  9. Reinstall the carburetor.
  10.  
  11. Operate the engine until it reaches normal operating temperatures. Be sure the choke is fully open, and the air cleaner is installed. If equipped, turn the air conditioner OFF .
  12.  
  13. Disconnect the plug the distributor vacuum, the canister purge and EGR vacuum lines. Shut off the vacuum to the idle compensator by bending the rubber hose.
  14.  
  15. Connect a dwell meter (4 cyl. scale) or duty meter to the duty monitor lead.
  16.  
  17. Turn the idle mixture screw all the way in and back out 1 1 / 2 turns.
  18.  
  19. Turn the throttle adjusting screw until the engine speed is 950 rpm (1986 and 1987) or 900 rpm (1988-90). Also refer to the Tune-Up Specification Chart in this section.
  20.  
  21. Adjust the idle mixture screw to achieve an average dwell of 36and#x00B0; or duty of 40 percent.
  22.  


NOTE
The dwell or duty reading specified is the average of the most constant variation.

  1. Reset the throttle adjusting screw until the engine speed is 850 and 19950 rpm.
  2.  
  3. Reinstall a mixture adjustment plug.
  4.  



Click image to see an enlarged view

Fig. Removing the mixture screw plug carbureted engines except 4XC1-U



Click image to see an enlarged view

Fig. Idle mixture screw concealment plug removal 4XC1-U engine



Click image to see an enlarged view

Fig. Before checking idle, disconnect the VSV pressure regulator 1983 and 1988 EFI Impulse



Click image to see an enlarged view

Fig. Idle speed adjusting screw 1983- and 1988 Impulse with G200Z, 4ZD1 and 4ZC1-T

 
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