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1974 Models

  1. Connect tachometer to engine. Start and warm engine to normal operating temperature. Stop engine and remove air cleaner. Disconnect vacuum sensing tube between servo diaphragm and vacuum control valve (at servo diaphragm).
  2. Remove intake manifold plug and connect servo diaphragm directly to intake manifold. Start engine and note engine speed. Engine speed should be 1300-1500 RPM (1100-1300 RPM on 808 models). If not, turn throttle opener adjusting screw.
  3. Stop engine, reconnect vacuum hoses to original locations, and attach vacuum gauge to intake manifold. Start and raise engine speed to 3000 RPM. Release throttle and allow RPM to drop suddenly.
  4. Turn vacuum control valve adjusting screw so that engine speed decreases from 3000 RPM to 1000 RPM above 22 in. Hg. Vacuum gauge should remain stationary for a few seconds at 1000 RPM and then fall to normal idle vacuum.
  5. To test vacuum switch, disconnect sensing tube from vacuum switch. Using a "T" fitting, connect a vacuum gauge in vacuum line. Connect one end of tube to vacuum source and increase vacuum to at least 6 in. Hg. Allow vacuum to drop. If switch does not "click" at about 3 in. Hg, replace vacuum switch.
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