Idle Mixture, Adjust

The dwell signal from the Computer Command Control (C-3) system is used to adjust idle mixture. Idle mixture should only be adjusted if carburetor is overhauled, or if "Diagnostic Checks" indicate the carburetor as source of complaint. The Mixture Control (MC) solenoid should not be adjusted.
1. Connect dwell meter to test lead in MC solenoid harness (usually a green wire) and set meter on 6 cylinder scale. Connect tachometer to engine following manufacturer's instructions.
2. Disconnect and plug purge hose at vapor canister and other hoses as directed by underhood Emission Control Label.
3. Start engine and run at fast idle until it reaches normal operating temperature, and dwell begins to fluctuate.
4. Place transmission in drive (manual transmission in neutral) and adjust curb idle speed to specifications.
5. Observe dwell meter, if reading fluctuates within 10 to 50 degree range, mixture adjustment is correct. Proceed to step 12.
6. If reading does not fluctuate, or if reading is not within 10 - 50 degree range, remove concealment plug sealing mixture screw as outlined in the Holley 6510-c chapter of the carburetor section.
7. Reinstall carburetor with air cleaner off and hoses plugged as in step 2. Turn mixture screw in (clockwise) until lightly seated, then back screw out 2 turns.
8. Start engine and run until it reaches normal operating temperature (dwell reading fluctuates).
9. Place transmission in drive (manual transmission in neutral). Adjust idle mixture screw, turning in small increments, to obtain a fluctuating dwell reading within 25 - 35 degree range, as close to 30 degrees as possible.
10. If unable to obtain specified dwell reading, repair carburetor idle circuit.
11. Install air cleaner and adjust curb idle speed to specifications.
12. Stop engine. Reconnect vacuum hoses to proper fittings and seal mixture screw cavity with RTV sealer.

4-97.6 EXCEPT NOVA

The dwell signal from the computer command control (C-3) system is used to adjust idle mixture. Idle mixture should only be adjusted if carburetor is overhauled, or if ``Diagnostic Checks'' indicate the carburetor as the source of complaint. The mixture control (MC) solenoid should not be adjusted.
1. Remove concealment plug as outlined in the Holley 6510-C chapter of the carburetor section.
2. Reinstall carburetor, then torque retaining nuts to 25 ft. lbs.
3. Connect fuel and vacuum lines, accelerator linkage, then the electrical connectors. Do not install air cleaner and gasket.
4. Connect a suitable dwell meter to mixture control dwell connector, with dwell meter set to 6-cylinder scale.
5. Connect a suitable tachometer to engine according to manufacturer's instructions, then block drive wheels and set parking brake.
6. Start and idle engine until system is in closed loop mode (Dwell needle varies). On a normal operating engine the dwell meter at both idle and part throttle will vary between 10° and 50°. This is closed loop operation, which means the oxygen sensor affects control of fuel delivery.
7. Place transmission selector lever in Drive on models with automatic transmission or Neutral on models with manual transmission.
8. If necessary, adjust idle mixture needle to obtain a dwell reading that varies between 25° and 35°, but as close to 30° as possible.
9. Install air cleaner and adjust idle speed as previously described.
10. Stop engine, then seal idle mixture needle cavity with a suitable sealant.