Engines produced by several GM divisions are used. The vehicle emission control information sticker in the engine compartment should be checked for the individual engine specifications.
- With the engine at normal operating temperature, set the parking brake and block the wheels.
- Remove the air cleaner to gain access to the idle air screws, but leave the vacuum lines connected.
- Disconnect and plug the other vacuum lines as indicated by the emission control sticker.
- Connect a tachometer and timing light to the engine, and if necessary, adjust the ignition timing to specifications. Disconnect the vacuum advance line, if directed by the instructions on the emission control sticker.
- Carefully remove the idle mixture screw limiter caps. Lightly seat the screws by turning them into the carburetor base, and then back the screws out equally until the engine will run without stalling.
- If the car has automatic transmission, place the selector lever in Drive.
- Back out the idle mixture screws, 1 / 8 of a turn at a time, until the maximum idle speed is obtained.
- Adjust the engine idle speed to 25-50 rpm over the specified low rpm setting. Repeat step 7, if necessary.
Two idle speed adjustments are normally required. One is the normal rpm setting, controlled by the adjustment of the electric solenoid screw, and the second adjustment, or low setting, is controlled by a screw on the carburetor throttle shaft lever. If the car has air conditioning, the solenoid may be used as an idle speed up control. To determine the type used, turn the air conditioning on; if the engine idle speed increases, the solenoid is used as a speed up device. The idle speed setting is then adjusted by the screw on the throttle shaft lever.
- Turn each screw in, 1 / 8 of a turn at a time, until the idle speed reaches the specified idle rpm.
- Reset the idle speed.
- Connect all the vacuum lines and install the air cleaner. Recheck the idle speed and correct as necessary.