Jeep CJ/Scrambler 1971-1986 Repair Guide

Idle Speed and Mixture Adjustments 1975-86

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1975-78

See Figures 1 through 9


WARNING
On vehicles equipped with a catalytic converter, do not idle the engine over three minutes at a time! If the adjustments are not completed within three minutes, run the engine at 2000 rpm for one minute.

  1. Turn the idle screw(s) to the full rich position. Note the position of the screw head slot inside the limiter cap slots.
  2.  
  3. Remove the limiter cap(s) carefully with a pair of needlenosed pliers. Reset the idle speed screws to the approximate position before cap removal.
  4.  
  5. Connect an accurate tachometer to the engine according to the manufacturer's instructions.
  6.  
  7. Run the engine to operating temperature.
  8.  
  9. Adjust the idle to 30 rpm above the recommended idle speed.
  10.  
  11. On V8 engines with automatic transmissions, the throttle stop solenoid is used to adjust the idle speed. Use the following procedure for these vehicles. On all other engines proceed to the next numbered step.
    1. With the solenoid wire connected, loosen the locknut and turn the solenoid in or out to obtain the specified rpm.
    2.  
    3. Tighten the solenoid bracket.
    4.  
    5. Disconnect the solenoid wire and adjust the idle speed screw to 500 rpm. Connect the wire.
    6.  

  12.  
  13. Starting from the full rich stop position (established before the limiters were removed), turn the mixture screws clockwise (leaner) until a slight rpm drop is indicated.
  14.  
  15. Turn the mixture screws counterclockwise until the highest rpm reading is obtained at the best lean idle setting. On carburetors with two screws, turn them evenly in alternating equal increments.
  16.  

If the idle speed changed more than 30 rpm during the adjustment, reset it to 30 rpm above the specified rpm and repeat the adjustment.

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Fig. Fig. 1: Autolite/Motorcraft 2100 carburetor, right side view



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Fig. Fig. 2: Autolite/Motorcraft 2100 carburetor, left side view



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Fig. Fig. 3: BBD 2-bbl carburetor adjusting points

1979-80

The procedure for adjusting the idle speed and mixture is called the lean drop procedure and is made with the engine operating at normal operating temperature and the air cleaner in place as follows:

  1. Turn the mixture screws to the full rich position with the tabs on the limiters against the stops. Note the position of the screw head slot inside the limiter cap slots.
  2.  
  3. Remove the idle limiter caps by threading a sheet metal screw in center of the cap and turning clockwise. Discard the limiter caps.
  4.  
  5. Reset the adjustment screws to the same position noted before the limiter caps were removed.
  6.  
  7. Start the engine and allow it to reach normal operating temperature.
  8.  
  9. Adjust the idle speed to 30 rpm above the specified rpm. See the Tune-Up Specifications chart. On 6-cylinder engines with a throttle stop solenoid, turn the solenoid in or out to obtain the specified rpm. On V8 engines with a throttle stop solenoid, turn the hex screw on the throttle stop solenoid carriage to obtain the specified rpm. This is done with the solenoid wire connected. Tighten the solenoid locknut, if so equipped. Disconnect the solenoid wire and adjust the curb idle speed screw to obtain an idle speed of 500 rpm. Reconnect the solenoid wire.
  10.  
  11. Starting from the full rich stop position, as was determined before the limiter caps were removed, turn the mixture adjusting screws clockwise (leaner) until a loss of engine speed is noticed.
  12.  
  13. Turn the screws counterclockwise (richer) until the highest rpm reading is obtained at the best lean idle setting. The best lean idle setting is on the lean side of the highest rpm setting without changing rpm.
  14.  
  15. If the idle speed changed more than 30 rpm during the mixture adjustment procedure, reset the idle speed to 30 rpm above the specified rpm with the idle speed adjusting screw or the throttle stop solenoid and repeat the mixture adjustment.
  16.  
  17. Install new limiter caps over the mixture adjusting screws with the tabs positioned against the full rich stops. Be careful not to disturb the idle mixture setting while installing the caps.
  18.  

1981-82

Idle mixture screws on these carburetors are sealed with plugs or dowel pins. A mixture adjustment must be undertaken ONLY when the carburetor is overhauled, the throttle body replaced, or the engine does not meet required emission standards. Since expensive testing equipment is needed to properly set the mixture, only the idle speed adjusting procedure is given below.

The adjustment is made with the manual transmission in neutral and the automatic in drive. Therefore, make certain that the vehicle's parking brake is set firmly, and that the wheels are blocked. It may be a good idea to have someone in the vehicle with their foot on the brake.

  1. Connect a tachometer, start engine and warm it to normal operating temperature. The choke and intake manifold heater (6-cylinder engine only) must be off.
  2.  
  3. If the engine speed is not within the OK range, turn the curb idle adjustment screw to obtain the specified curb idle rpm.
  4.  
  5. For the 6-cylinder engine (BBD carburetor): Disconnect the vacuum hose from the vacuum actuator and holding solenoid wire connector. Adjust the curb (slow) idle speed adjustment screw to obtain the specified curb (slow) idle rpm, if it is not within the OK range. Refer to the Emission Control Information label, and the Tune-Up Specifications Chart. Apply a direct source of vacuum to the vacuum actuator. Turn the vacuum actuator adjustment screw on the throttle lever until the specified rpm is obtained (900 rpm for manual transmissions, and 800 rpm for automatic transmissions). Disconnect the manifold vacuum source from the vacuum actuator. With the jumper wire, apply battery voltage (12v) to energize the holding solenoid. Turn the A/C on, if equipped.
  6.  

The throttle must be opened manually to allow the Sol-Vac throttle positioner to be extended.

With the Sol-Vac throttle positioner extended, the idle speed should be 650 rpm for automatic transmission equipped vehicles and 750 rpm for manual transmission equipped vehicles. If the idle speed is not within tolerance, adjust the Sol-Vac (hex-head adjustment screw) to obtain the specified rpm. Remove the jumper wire from the Sol-Vac holding solenoid wire connector. Connect the Sol-Vac holding solenoid wire connector. Connect the original hose to the vacuum actuator.

  1. For four and eight cylinder engines (2SE, E2SE or 2150 carburetor), turn the nut on the solenoid plunger or the hex screw on the solenoid carriage to obtain the specified idle rpm. Tighten the locknut, if equipped. Disconnect the solenoid wire connector and adjust the curb idle screw to obtain a 500 rpm idle speed. Connect the solenoid wire connector. If the model 2150 carburetor (8-cylinder engine), is equipped with a dashpot, fully depress the dashpot stem with the throttle at the curb idle position, and measure the clearance between the stem and throttle lever. The clearance should be 0.032 in. (0.8mm). Adjust it by loosening the locknut and turning the dashpot.
  2.  

1983-84 4-150

  1. Fully warm up the engine.
  2.  
  3. Check the choke fast idle adjustment: Disconnect and plug the EGR valve vacuum hose. Position the fast idle adjustment screw on the second step of the fast idle cam with the transmission in neutral. Adjust the fast idle speed to 2,000 rpm for manual transmission and 2,300 rpm for automatic transmission. Allow the throttle to return to normal curb idle and reconnect the EGR vacuum hose.
  4.  
  5. To adjust the Sol-Vac Vacuum Actuator: Remove the vacuum hose from the vacuum actuator and plug the hose. Connect an external vacuum source to the actuator and apply 10-15 inches Hg of vacuum to the actuator. Shift the transmission to Neutral. Adjust the idle speed to the following rpm using the vacuum actuator adjustment screw on the throttle lever: 850 rpm for automatic transmission 950 rpm for manual transmission. The adjustment is made with all accessories turned off.
  6.  

The curb idle should always be adjusted after vacuum actuator adjustment.

  1. To adjust the curb idle: Remove the vacuum hose from the Sol-Vac vacuum actuator and plug the hose. Shift the transmission into Neutral. Adjust the curb idle using the 1 / 4 in. (6mm) hex-head adjustment screw on the end of the Sol-Vac unit. Set the speed to 750 rpm for manual transmission, 700 rpm for automatic transmission. Reconnect the vacuum hose to the vacuum actuator.
  2.  

Engine speed will vary 10-30 rpm during this mode due to the closed loop fuel control.

  1. To adjust the TRC (Anti-Diesel): The TRC screw is preset at the factory and should not require adjustment. However, to check adjustment, the screw should be 3 / 4 turn from closed throttle position.
  2.  

1983-84 6-258

SOL-VAC Vacuum Actuator Adjustment
  1. Disconnect and plug the vacuum hose to the Sol-Vac vacuum actuator.
  2.  
  3. Disconnect the Sol-Vac electrical connector. Connect an external vacuum source to the vacuum actuator and apply 10-15 inches Hg of vacuum.
  4.  
  5. Open throttle for at least 3.0 seconds (1200 rpm); then close throttle.
  6.  
  7. Set the speed using the vacuum actuator adjustment screw on the throttle lever to obtain specified rpm.
  8.  
  9. Disconnect the external vacuum source. Reconnect the Sol-Vac vacuum hose and electrical connector.
  10.  

SOL-VAC Holding Solenoid Adjustment

The Sol-Vac vacuum actuator adjustment should always precede the Sol-Vac solenoid adjustment.

  1. Disconnect and plug the vacuum hose at the Sol-Vac vacuum actuator.
  2.  
  3. Disconnect the Sol-Vac electrical connector.
  4.  
  5. Energize the Sol-Vac holding solenoid with either of the two following methods:
    1. Apply battery voltage (12v) to the solenoid, or,
    2.  
    3. Reconnect the Sol-Vac electrical connector and turn on the rear window defogger or turn on the air conditioner with the compressor disconnected.
    4.  

  6.  
  7. Open throttle for at least 3.0 seconds (1,200 rpm) to allow the Sol-Vac holding solenoid to fully extend.
  8.  
  9. Set the speed using the 1 / 4 in. (6mm) hex-head adjustment screw on the end of the Sol-Vac unit to obtain the specified rpm.
  10.  
  11. Reopen the throttle above 1,200 rpm to insure the correct holding position and reset the speed if necessary. Reconnect the vacuum hose to the Sol-Vac actuator. Reconnect the Sol-Vac electrical connector if disconnected.
  12.  



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Fig. Fig. 4: Adjusting the fast idle speed screw



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Fig. Fig. 5: Turn the nut at the back of the throttle stop valve

1985-86 4-150 with YFA CARBURETOR

  1. The TRC (anti-Diesel) adjustment screw is statically set at 3 / 4 of turn from the throttle valve closed position during factory assembly and does not normally require readjustment. Should this adjustment be required, turn the adjustment screw counterclockwise to the throttle plate closed position and then turn the screw clockwise 3 / 4 turn.
  2.  
  3. Connect a tachometer to the ignition coil TACH wire connector.
  4.  
  5. Place the transmission in NEUTRAL and lock the parking brake.
  6.  
  7. Start the engine and allow it to reach normal operating temperature.
  8.  
  9. Connect an external vacuum source to the Sol-Vac vacuum actuator and apply 10-15 in.Hg of vacuum. Plug the engine vacuum hose.
  10.  
  11. Adjust the vacuum actuator until an engine speed of approximately 1,000 rpm is achieved.
  12.  

Refer to the Vehicle Emission Control Information Label for the latest specifications for the particular engine being adjusted.

  1. Remove the vacuum source from the vacuum actuator and retain the plug in the vacuum hose from the engine.
  2.  
  3. Turn the hex-head curb idle speed adjustment screw until the speed of 500 rpm is obtained.
  4.  

Refer to the Vehicle Emission Control Label for the latest specifications for the particular engine being adjusted.

  1. Stop the engine and connect the engine vacuum hose to the vacuum actuator.
  2.  
  3. Remove the tachometer from the engine.
  4.  



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Fig. Fig. 6: E2SE carburetor Idle speed adjustment, models without air conditioning



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Fig. Fig. 7: E2SE carburetor Idle speed adjustment, models with air conditioning



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Fig. Fig. 8: Some 1980 and later model 2150 carburetors have 2 piece metal plugs and caps in place of plastic limiter caps, on the idle mixture adjusting screws



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Fig. Fig. 9: Location of the idle adjustment points on the Motorcraft/Autolite 2100 and 2150 carburetors

1985-86 6-258

The carburetor choke and intake manifold heater must be off. This occurs when the engine coolant heats to approximately +160°F (71°C).

  1. Have the engine at normal operating temperature. Connect a tachometer to the ignition coil negative (TACH) terminal.
  2.  
  3. Remove the vacuum hose from the Sol-Vac vacuum actuator unit. Plug the vacuum hose. Disconnect the holding solenoid wire connector.
  4.  
  5. Adjust the curb (slow) idle speed screw to obtain the correct curb idle speed. Refer to the specifications under Idle Speed or refer to the Emission Information label, under the hood, for the correct curb idle engine rpm.
  6.  
  7. Apply a direct source of vacuum to the vacuum actuator, using a hand vacuum pump or its equivalent. When the Sol-Vac throttle positioner is fully extended, turn the vacuum actuator adjustment screw on the throttler lever until the specified engine rpm is obtained. Disconnect the vacuum source from the vacuum actuator.
  8.  
  9. With a jumper wire, apply battery voltage (12v) to energize the holding solenoid.
  10.  

The holding wire connector can be installed and either the rear window defroster or the air conditioner (with the compressor clutch wire disconnected) can be turned on to energize the holding solenoid.

  1. Hold the throttle open manually to allow the throttle positioner to fully extend.
  2.  

Without the vacuum actuator, the throttle must be opened manually to allow the Sol-Vac throttle positioner to fully extend.

  1. If the holding solenoid idle speed is not within specifications, adjust the idle using the 1 / 4 in. (6mm) hex-headed adjustment screw on the end of the Sol-Vac unit. Adjust to specifications.
  2.  
  3. Disconnect the jumper wire from the Sol-Vac holding solenoid wire connector, if used. Connect the wire connector to the Sol-Vac unit, if not connected. Install the original vacuum hose to the vacuum actuator.
  4.  
  5. Remove the tachometer and if disconnected, connect the compressor clutch wire. Install any other component that was previously removed.
  6.  

 
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