Component Testing: THERMOVALVE: Carbureted

1. With engine cold, start engine and check for vacuum to distributor diaphragm "B". Vacuum should be present. If vacuum is present, go to step 3).
2. If vacuum is not present, verify presence of manifold vacuum to thermovalve. If vacuum is present, verify proper routing of vacuum hoses. If hoses are routed correctly, replace thermovalve.
3. Warm engine to operating temperature (cooling fan comes on). Check for vacuum to distributor diaphragm "B". Vacuum should not be present. If vacuum is present, verify proper hose routing. If routing is correct and air cleaner bleed hose is not blocked, replace thermovalve.

Fig 1: EFI Timing Control System

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Fig 2: Carbureted Timing Control System

Courtesy of AMERICAN HONDA MOTOR CO., INC.