See Figures 1 and 2
The octane selector is used as a fine adjustment to match the vehicle's ignition timing to the grade of gasoline being used. It is located near the distributor vacuum unit (on models so equipped), beneath a plastic dust cover. Normally the octane selector should not require periodic attention, however should adjustment become necessary:
- Align the setting line with the threaded end of the housing and then align the center line with the setting mark on the housing.
- Drive the car to the specified speed for the octane selector test in High gear on a level road.
- Depress the accelerator pedal all the way to the floor. A slight pinging sound should be heard. As the car accelerates, the sound should gradually go away.
- If the pinging sound is low or if it fails to disappear as the vehicle speed increases, retard the timing by turning the knob toward R (Retard).
- If there is no pinging sound at all, advance the timing by turning the knob toward A (Advance).
On 1973-79 models, do not turn the octane selector more than1/2turn toward R. Do not turn it toward A at all
- When the adjustment is completed, install the plastic dust cover.
One graduation of the octane selector is equal to about 10 degrees of crankshaft angle