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Idle Mixture

NOTE: Mixture is not adjustable on models with fuel injection.
NOTE: Mixture adjustment is NOT a part of normal tune-up procedure and should not be performed unless mixture control unit is replaced or vehicle fails emissions testing. Specifications for all other models are not available.
  1. Remove carburetor. Drill 1/4" deep hole in idle mixture adjusting screw plug. See Fig 1 . Remove plug and install carburetor. Start engine and warm to normal operating temperature. Disconnect idle set connector ("CHECK ENGINE" light will come on).
  2. Connect positive lead of dwell meter to the duty monitor lead, and negative terminal to ground. Put dwell meter on 6-cylinder scale and adjust idle mixture until meter reads 30 degrees with engine at correct idle.
  3. Connect idle set connector ("CHECK ENGINE" light will go off). Check idle speed and adjust if necessary. Install new idle mixture plug. If duty cycle cannot be adjusted, check carburetor feedback system. See TESTS W/CODES or TESTS W/O CODES in this Section.
Fig 1: Removing Carburetor Idle Mixture Plug
G121578Courtesy of GENERAL MOTORS CORP.
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