Air/Fuel Mixture: Testing and Inspection

Inspection
Before adjusting idle speed or mixture, be sure the ignition timing, spark plugs, and carburetor float level are all in normal operating condition. Turn off all lights and other unnecessary electrical loads.
All adjustments must be made with the cooling fan motor not operating.


1. Warm up engine and run it at idle.

Fig. 23 Connecting Dwellmeter To A/F Solenoid Valve.:

2. Connect a dwellmeter (90 degrees, 4 cylinders) to the (BrY) wire in the check connector of the A/F solenoid.

Fig. 8 Idle Mixture Dwell Reading Range.:

3. Check the idle mixture (duty) at idle speed (800 - 850 rpm).

Idle mixture: 20 - 70 degrees.

NOTE: If the idle mixture is not within specifications, check the oxygen sensor, the control unit, and the wiring between the oxygen sensor and the control unit. If they are satisfactory, adjust the idle mixture.
4. Using a jumper wire, ground the A/F checking connector (BrY) and confirm that the engine speed drops.
5. If the engine speed doesn't drop, clean the A/F solenoid valve, or carburetor, or replace the air horn assembly.
NOTE: Clean by using gasoline and blowing out with compressed air or carburetor spray, but do not submerge in cleaner. A/F solenoid must be replaced with new air horn. A/F solenoid is not available separately.