Idle Mixture Adjustment

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.