This section contains only tune-up adjustment procedures for fuel systems. Descriptions, adjustments, and overhaul procedures for fuel system components can be found in the Fuel System section of Fuel System .
IDLE SPEED ADJUSTMENT 1957-74 Models
- Start the engine and run it until it reachers operating temperature.
- If it hasn't already been done, check and adjust the ignition timing. After you have set the timing, turn OFF the engine.
- Attach a tachometer to the engine.
- Remove the air cleaner, except on 1971 and later model engines. Leave the air cleaner on these models. Turn ON the headlights to high beam.
- Start the engine and, with the transmission in Neutral or Park, check the idle speed on the tachometer. If the reading on the tachometer is correct, turn OFF the engine and remove the tachometer. If it is not correct, proceed to the following steps.
- Turn the idle adjusting screw at the bottom of the carburetor with a screwdriver clockwise to increase idle speed and counterclockwise to decrease it.
MIXTURE ADJUSTMENT 1957-74 Models
See Figures 1, 2 and 3
The idle mixture screw is located at the very bottom of the carburetor.
- Turn the screw until it is all the way in. Do not force the screw in any further because it is very easy to damage the needle valve and its seat by screwing the adjusting screw in too tightly.
- Turn the screw out 3 / 4 to 1 3 / 4 turns. This should be the normal adjustment setting. For a richer mixture, turn the screw out. The ideal setting for the mixture adjustment screw results in the maximum engine rpm.
Limiter caps are installed on all carburetors on all 1971 and later American Motors engines and some pre-1971 engines. These caps limit the amount of adjustment that can be made and should not be removed, if possible. If a satisfactory idle cannot be obtained, however, they can be removed by installing a sheet metal screw in the center of the screw and turning clockwise. After removing the caps, adjust the carburetor in the same manner as was used without the caps. There are special service limiter caps available to replace the ones removed. Install the service limiter caps with the ears positioned against the full rich stops. Be careful not to disturb the idle setting while installing the caps. Press the caps squarely and firmly into place.
IDLE SPEED AND MIXTURE ADJUSTMENTS 1975-78 Models
See Figures 4 and 5
- Turn the idle screw(s) to the full rich position. Note the position of the screw head slot inside the limiter cap slots.
- Remove the limiter cap(s) carefully with a pair of needlenosed pliers. Reset the idle speed screws to the approximate position before cap removal.
- Connect an accurate tachometer to the engine according to the manufacturer's instructions.
- Run the engine to operating temperature.
- Adjust the idle to 30 rpm above the recommended idle speed.
On V8 engines with automatic transmissions, the throttle stop solenoid is used to adjust the idle speed. Use the following procedure for these vehicles:
- With the solenoid wire connected, loosen the locknut and turn the solenoid in or out to obtain the specified rpm.
- Tighten the solenoid bracket.
- Disconnect the solenoid wire and adjust the idle speed screw to 500 rpm. Connect the wire.
- 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.
- 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.
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.
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:
- 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.
- Remove the idle limiter caps by threading a sheet metal screw in center of the cap and turning clockwise. Discard the limiter caps.
- Reset the adjustment screws to the same position noted before the limiter caps were removed.
- Start the engine and allow it to reach normal operating temperature.
- 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.
- 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.
- 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.
- 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.
- 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.
See Figures 6, 7 and 8
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.
- 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.
- If the engine speed is not within the specified range, turn the curb idle adjustment screw to obtain the specified curb idle rpm.
- 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.
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.
- 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 (eight-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 inch. Adjust it by loosening the locknut and turning the dashpot.
1983 Models4-150 ENGINES
- Fully warm up the engine.
- 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.
- 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.
The curb idle should always be adjusted after vacuum actuator adjustment.
- 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. 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.
Engine speed will vary 10-30 rpm during this mode due to the closed loop fuel control.
- 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.
- Connect a tachometer to the ignition coil negative terminal or to the pigtail wire connector above the heater blower motor.
- Disconnect the plug the vacuum hose at the distributor vacuum advance.
- If necessary, adjust the ignition timing with the engine speed at or below specifications.
- Reconnect the vacuum hose to the distributor vacuum advance unit.
- Disconnect the deceleration valve hose and canister purge hose. Plug the hose and remove the air cleaner assembly.
- If equipped with air conditioning, turn the control switch to the ON position and open the throttle momentarily to insure the solenoid armature is fully extended. Adjust the solenoid idle speed adjusting screw to obtain the specified engine curb idle speed rpm. Turn the A/C control switch to the OFF position.
- If not equipped with A/C, adjust the engine idle speed rpm with the solenoid idle speed adjusting screw. Disconnect the solenoid wire and adjust the curb idle.
- Install the air cleaner assembly. Connect all hoses and other connections.
Some California vehicles using the V6 engine, are equipped with a 2,200 hour engine timer. The timer activates a solenoid to control operation of the carburetor secondary vacuum brake after 2,200 hours of vehicle operation. The timer is not a serviceable component and must not be disassembled. In the event of a timer malfunction, the complete engine wiring harness must be replaced.
- Connect a tachometer to the ignition system. Start the engine and operate to normal operating temperature.
- Turn OFF all accessories including the A/C system.
- Put the manual transmission equipped vehicles in Neutral and the A/T equipped vehicles in Drive with the parking brake locked and the wheels chocked.
- Adjust the curb idle speed adjusting screw to obtain the specified rpm of 700 for both manual and automatic transmission equipped vehicles.
- Disconnect the vacuum hose from the idle kick actuator and connect an outside vacuum source to the actuator. Apply 15 in.Hg. of vacuum to the actuator.
- Adjust the actuator hexhead adjustment screw for the specified 1,200 rpm with both types of transmissions in the Neutral position.
- Stop the engine, remove the tachometer and vacuum pump. Install the vacuum hose to the actuator.
6-258 ModelsSOL-VAC VACUUM ACTUATOR ADJUSTMENT
- Disconnect and plug the vacuum hose to the Sol-Vac vacuum actuator.
- Disconnect the Sol-Vac electrical connector. Connect an external vacuum source to the vacuum actuator and apply 10-15 inches (Hg.) of vacuum.
- Open throttle for at least 3.0 seconds (1200 rpm); then close throttle.
- Set the speed using the vacuum actuator adjustment screw on the throttle lever to obtain specified rpm.
- Disconnect the external vacuum source. Reconnect the Sol-Vac vacuum hose and electrical connector.
See Figure 9
The Sol-Vac vacuum actuator adjustment should always precede the Sol-Vac solenoid adjustment.
- Disconnect and plug the vacuum hose at the Sol-Vac vacuum actuator.
- Disconnect the Sol-Vac electrical connector.
Energize the Sol-Vac holding solenoid with either of the two following methods:
- Apply battery voltage (12v) to the solenoid, or,
- Reconnect the Sol-Vac electrical connector and turn on the rear window defogger or turn on the air conditioner with the compressor disconnected.
- Open throttle for at least 3.0 seconds (1,200 rpm) to allow the Sol-Vac holding solenoid to fully extend.
- Set the speed using the 1 / 4 " hex-head adjustment screw on the end of the Sol-Vac unit to obtain the specified rpm.
- 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.
See Figure 10
If the vehicle is equipped with automatic transmission, lock the parking brake, chock the wheels and place the selector lever in Drive position before adjusting the idle speed.
- Connect a tachometer to the ignition coil negative terminal.
- Start the engine and allow it to reach normal operating temperature.
- Turn the hex-head adjustment screw on the solenoid carriage to obtain the correct engine speed of 600 rpm. (Verify from Emission Control label, located under the engine hood).
- Disconnect the solenoid wire connector and adjust the curb idle speed screw to obtain 500 rpm. (Verify from emission control label, located under the engine hood).
- Reconnect the solenoid wire connector and stop the engine.
- If equipped with a dashpot, position the throttle at the curb idle position and depress the dashpot stem.
- Measure the clearance between the stem and the throttle lever. A clearance of 0.032 in. should exist.
- Adjust the clearance as required by loosening the locknut and turning the dashpot until the correct clearance is obtained. Tighten the dashpot locknut.