Adjustments should be performed with the air cleaner removed and, on models so equipped, with the air conditioning turned off.
- Remove the air cleaner.
- Connect a tachometer and vacuum gauge to the engine, set the parking brake, and place the transmission in neutral.
- Turn in the idle mixture screws until they seat gently, then back them out 1 1 / 2 turns.
- Start the engine and allow it to reach normal operating temperature. Make sure that the choke is fully open, then adjust the idle speed (automatic in Drive, manual in neutral).
- Adjust the idle mixture screw(s) to obtain the highest steady vacuum at the specified idle speed, except for the Rochester BV. For this carburetor, adjust the idle mixture screw out 1 / 4 turn from the lean "drop off," the point where a 20-30 rpm drop is achieved by leaning the mixture.
On carburetors having a hot idle compensator valve (air-conditioned models), hold the brass valve down with a pencil while making the mixture adjustment.
- Repeat steps four and five if necessary.
- Turn off the engine, remove the gauges, and install the air cleaner.