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1977 Models (Vacuum Control Valve Test)

  1. Connect tachometer to engine. Start and warm engine to normal operating temperature. Stop engine and remove air cleaner. Disconnect and plug vacuum hose from anti-afterburn valve. Connect vacuum gauge to intake manifold. See Figure.
  2. Start engine. Increase engine speed to 3000 RPM and quickly release throttle. Vacuum gauge highest reading should be obtained immediately after releasing throttle, drop to 22-23 in. Hg, and then slowly drop to idle vacuum.
  3. If vacuum reading is incorrect, turn adjusting screw in vacuum control valve. Decrease vacuum reading by turning screw clockwise; increase by turning screw counterclockwise.
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