Vacuum Switch

With the cap of the leading ignition distributor removed, remove vacuum sensing tube from the vacuum advance tube of the distributor and attach a vacuum gauge in its place. Proceed as follows:

1. Hold mouth to tube of vacuum gauge and suck in. Watch vacuum gauge and listen for the vacuum switch to change from ON to OFF at approximately 7.09 in. (180 mm) Hg. Vacuum switch should then change from OFF to ON when vacuum is reduced to approximately 4.72 in. (120 mm) Hg.
2. Replace distributor cap and replace vacuum sensing tube to the vacuum advance of the distributor. Remove thermosensor connector and connect timing light to the high tension lead of the trailing distributor.
3. Run engine at idle speed and then raise RPM. Timing light should stop flashing when speed is raised to between 1600-4200 RPM.
   Fig 1: Testing Vacuum Switch

   Courtesy of MAZDA MOTORS CORP.