Carbureted Engine

With Engine Cold

Engine coolant temperature should be below 140°F and intake air temperature should be below intake air temperature switch set temperature. Switch should have continuity.
1. Disconnect vacuum hose No. 8 from vacuum advance diaphragm B on distributor, then connect suitable vacuum gauge to hose.
2. Start engine and allow to idle. If vacuum is present, test system with engine hot. If vacuum is not present, check for voltage at vacuum control solenoid valve blue/black wire connector in emission box.
3. If voltage is present, replace vacuum control solenoid valve and repeat test. If voltage is not present, refer to Troubleshooting.

With Engine Hot

1. Disconnect vacuum hose No. 8 from vacuum advance diaphragm B on distributor, then connect suitable vacuum gauge to hose.
2. Start engine and allow to reach normal operating temperature. At idle, vacuum should not be present.
3. If vacuum is not present, proceed to step 5. If vacuum is present, check for voltage at vacuum control solenoid valve blue/black wire connector in emission control box.
4. If voltage is present, refer to Troubleshooting. If voltage is not present, replace vacuum control solenoid valve and repeat test.
5. Attach hand vacuum pump to vacuum advance diaphragms A and B using a suitable T-fitting.
6. Plug ends of advance hoses, then pinch off hose to diaphragm B.
7. Start engine, apply 16 inches Hg vacuum and record timing. Timing should advance and remain steady.
8. If timing advances, proceed to step 9. If timing will not stay advanced, replace advance diaphragm and repeat test. If timing does not advance, stop engine and remove distributor cap. Inspect breaker plate for free movement. If no binding is evident, replace advance diaphragm and repeat test.
9. Release pinched hose and apply 16 inches Hg vacuum. Timing should advance more than recorded in step 7 and remain steady.
10. If timing advances more than previous test, system is satisfactory. If timing does not advance more than recorded in step 7, replace advance diaphragm and repeat test.