Air/Fuel Mixture: Adjustments
NOTE: Before performing idle mixture adjustment, remove idle mixture adjusting screw concealment plug as described under "Conceal Plug Removal" in the "Carburetor Section".Fig. 2 Idle mixture adjusting tool modifications:
EXCEPT CALIFORNIA MODELS
NOTE: The following adjustment should be performed with the air cleaner in place.
1. Connect suitable tachometer, then start engine and allow to reach operating temperature.
2. On models with automatic transmission, place selector lever in drive. On models with manual transmission, place selector lever in neutral. Apply parking brake and block drive wheels.
3. Check curb idle speed and adjust as necessary, refer to "Curb Idle Speed, Adjust".
4. Using idle mixture socket tool J-29030, modified as shown in Fig. 2., turn mixture adjusting clockwise until a loss in RPM is noted.
5. Turn idle mixture adjusting counterclockwise until the highest engine RPM is obtained.
6. Turn idle mixture adjusting clockwise until a 20 RPM drop in engine RPM is obtained.
7. If final idle speed differs more than 30 RPM from the original curb idle speed, adjust curb idle speed and repeat steps 4 through 6.
Fig. 2 Idle mixture adjusting tool modifications:
CALIFORNIA MODELS
Pre-Set Procedure
1. Remove carburetor from engine, then idle mixture adjusting screw concealment plug
2. Turn idle mixture screw clockwise until lightly seated, the back screw out 4 turns.
3. Check to ensure idle air bleed plug is installed in air horn.
4. Remove vent stack screen to gain access to lean mixture adjusting screw located in bottom of fuel bowl.
5. Turn lean mixture adjusting screw clockwise until lightly seated, the back screw out 2-1/2 turns.
6. Modify tool No. J-29030-B, by grinding 1/8 inch off rear and 1/4 inch off front of tool, Fig. 2. Install carburetor with modified tool position on idle mixture adjusting screw.
7. Leave bowl vent, EGR and canister purge hoses disconnected and cap hose connections carburetor.
8. Locate hose from carburetor port to to temperature sensor and secondary vacuum break thermal vacuum switch. Disconnect and plug this hose at temperature sensor on air cleaner.
9. Connect positive lead of suitable dwell meter to Mixture Control (MC) solenoid dwell test wire (green connector) at carburetor. Connect dwell meter negative lead to ground, then set meter to 6 cylinder scale.
10. Connect tachometer to distributor wire (brown connector). If equipped with tachometer, connect test tachometer lead to distributor side of tach filter.
11. Place transmission in neutral, with parking brake applied and drive wheels blocked.
Mixture Adjustment Procedure
1. Start engine and allow to operate at fast idle for at least 3 minutes.
2. Bring engine speed to 3000 RPM, then adjust lean mixture screw to an average dwell reading of 35°. Turn adjusting screw in small increments, allowing dwell to stabilize. The dwell meter may cycle as much as 15 degrees, therefore it is necessary to obtain an average dwell reading. To increase dwell turn screw back screw out. To decrease dwell, turn screw in. If specified average dwell reading cannot be obtained, check main metering system for leaks and restrictions.
3. Return engine top curb idle.
4. Adjust idle mixture screw using modified tool J-29030-B, until an average dwell reading of 25° is obtained. Turn adjusting screw in small increments, to allow dwell to stabilize. The dwell meter may cycle as much as 5 degrees, therefore it is necessary to obtain an average dwell reading. To increase dwell, back screw out. To increase dwell turn screw in. If specified average dwell cannot be obtained, check idle system for leaks and restrictions.
5. Remove adjusting tool from idle mixture adjusting screw and recheck dwell reading.
6. Disconnect MC solenoid electrical connector and check for engine speed change of at least 50 RPM. If RPM does not change sufficiently, check idle air bleed circuit leaks and restrictions.
7. Operate engine at 3000 RPM and check for an average dwell reading of 35°. If average dwell reading is 35°, no further adjustment is required. If average dwell reading is not 35°, repeat steps 2 through 6.
8. After completing adjustments, seal idle mixture screw openings with RTV sealer and install or connect all components removed.
9. If necessary, readjust idle speed.