Ignition Timing: Adjustments

SET IGNITION TIMING

1. Connect a suitable Timing Light to #1 cylinder or a magnetic timing unit (use a 10~ offset when required).
Do not puncture cables, boots or nipples with the test probes. Always use proper adapters. Puncturing the spark plug cables with a probe will damage the cables. The probe can separate the conductor and cause high resistance. In addition breaking the rubber insulation may permit secondary current to arc to ground.
2. Connect red lead of the test tachometer unit to the negative primary terminal of the coil and the black lead to a good ground.
3. Turn selector switch to the appropriate cylinder position.
4. Start engine and run until operating temperature is obtained.
5. With engine at normal operating temperature (off fast idle), momentarily open the throttle and release to make sure there is no bind in the linkage and that idle speed screw is against its stop.
6. On vehicles equipped with a carburetor switch, connect a jumper wire between the carb switch and ground. Disconnect and plug the vacuum line at the Spark Control Computer.
7. Read engine rpm on 1000 rpm scale. If the engine rpm is at or below the curb idle specified on the label, proceed to the next step. If it is higher, turn the idle speed screw (on top of solenoid) until the specified curb idle rpm is reached.
8. Aim Timing Light at timing hole in bell housing, or read magnetic timing unit. If flash occurs when timing mark is before specified degree mark, timing is advanced. To adjust, turn distributor housing in direction of rotor rotation. If flash occurs when timing is within +/- 2~ of value specified on the label, proceed to step (10). If outside specified tolerance proceed to next step.
9. Loosen distributor hold-down arm screw just enough so the distributor housing can be rotated in its mounting. Turn distributor housing until specified label value is reached. Tighten the hold-down arm screw and recheck timing. When timing is acceptable, recheck curb idle rpm. If engine rpm is not at or below the curb idle rpm shown on the label, reset engine rpm and recheck timing. Repeat above until both engine rpm and timing are acceptable.
10. Remove timing lamp or magnetic timing unit. Unplug and reconnect the vacuum hose to the SCC unit.
11. If curb idle speed is not within +/- 50 rpm of value shown on label, readjust curb idle rpm. Do not reset timing.
12. Turn the engine off. Remove the jumper wire, and tachometer.