Spark Control System (Spk)

Fig. 133 Timing Light Hookup And Aiming:

NOTE: Perform ignition timing inspection with the engine at normal operating temperature (cooling fan should cycle on and off at least once).
1. Remove the rubber cap from the timing window of the cylinder block.
2. Connect a timing light to the engine, Fig. 133.

Fig. 134 Clamp Both Vacuum Advance Lines:

3. Disconnect the vacuum hoses from the vacuum advance diaphragm and pinch the end of the hoses closed, Fig. 134.

Ignition timing should be 4° BTDC

Fig. 136 Distributor Hold-Down Bolt Locations (Carbureted Engine):

4. If the ignition timing is not within specifications, adjust it by loosening the distributor adjustment bolts, Fig. 136, and turning the distributor housing:
Counter-clockwise to advance.
Clockwise to retard.
5. After adjusting, re-tighten the adjustment bolts and re-check the timing.

Fig. 138 Checking Vacuum To Advance Diaphragm 'A' (Carbureted Engine):

6. Unplug the #2 vacuum hose, Fig. 138, and connect a vacuum gauge to the hose. With the engine at idle, vacuum should be at least 500 mbar (15 in. Hg). If the vacuum reading is not within specifications;
a. Check the hoses for correct routing, cracks, or bad connections.
b. Check the vacuum port in the intake manifold for blockage.
7. Connect the #2 vacuum hose to the advance diaphragm on the distributor.

Ignition Timing Inspection Windows:

8. With the engine at idle, point the timing light at the timing window, Fig. 139. The ignition timing should be:

Manual Transmission (at 800 +/- 50 rpm, in neutral)
49 State/High altitude 24° +/- 2° BTDC (red)
California 20° +/- 2° BTDC (red)

Automatic Transmission (at 730 +/- 50 rpm, in gear)
49 State/ High altitude 15° +/- 2° BTDC (red)
California 15° +/- 2° BTDC (red)

9. If the ignition timing does not advance as specified, check the vacuum advance diaphragm.

Fig. 141 Checking Vacuum To Advance Diaphragm 'B' (Carbureted Engine):

10. Unplug the #25 vacuum hose and connect a vacuum gauge to the hose, Fig. 141. With the engine at idle, check for vacuum. No vacuum should be available. If vacuum is available, replace thermovalve B and re-test.
NOTE: Thermovalve B opens at 50°C (122°F). On a cold engine, there should be no vacuum at the #25 vacuum hose with the engine at idle.