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Orifice Spark Advance Control: Testing

  1. Inspect all hoses for leakage or damage. Replace as necessary.
  2. Warm engine to normal operating temperature. Tee a vacuum gauge into red hose at OSAC valve leading to distributor.
  3. Set parking brake and run engine at 2000 RPM in neutral.
  4. Vacuum should increase gradually (about 20 seconds) to a stable level. Time will vary with different engines.
  5. If vacuum rises immediately to same level as manifold vacuum, OSAC valve is not operating properly, and must be replaced. If there is NO increase in vacuum, OSAC valve is defective and must be replaced.
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