Carbureted Engine

With Engine Cold

Engine coolant temperature should be below thermovalve set temperature.
1. Disconnect vacuum hose from vacuum advance diaphragm B on the distributor and connect suitable vacuum gauge to the hose.
2. Start engine and allow to idle. If vacuum is present, test system with engine hot. If vacuum is not present, replace thermovalve.

With Engine Hot

1. Connect suitable tachometer, then disconnect vacuum hose No. 2 from the vacuum advance diaphragm B on the distributor and connect a vacuum gauge to the hose.
2. Start engine and allow to idle. If vacuum is not present, proceed to step 3. If vacuum is present, replace thermovalve.
3. Connect suitable hand vacuum pump to vacuum advance diaphragms A and B by using a T-fitting.
4. Plug ends of the advance hoses, then pinch off hose to diaphragm B.
5. Start engine, then apply 16 inches Hg. If timing advances, proceed to step 6. If timing will not stay advanced, replace advance diaphragm. If timing does not advance, stop engine and remove distributor cap. Inspect breaker plate for free movement. If no binding is present, replace advance diaphragm.
6. Release pinched hose and apply 16 inches Hg. If timing advances more than recorded in step 5, test is complete. If timing does not advance more than recorded in step 5 or will not stay advanced, replace advance diaphragm.