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OT: 4 Gauge Vacum set for MC

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  • OT: 4 Gauge Vacum set for MC

    What is the basic construction of these units, are they just 4 simple and separate gauges in a bracket ?

  • #2
    Yes they are Ken, of course the better gauge sets have dampers built in to minimize the vacuum fluctuations inherent in a separate carb per cylinder engine.
    The trick is to get all four to read the same.
    If the engine is in good mechanical shape and the mixture and the throttle positions equal the vacuum should be equal on each cylinder.

    Here are two examples.
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia


    • #3
      Yes, with shut off valves for each gauge to help settle the needle fluctuations. I recently gave away a set of "mercury sticks". Very simple construction consisting of 4 glass tubes mounted in a graduated "board" about 3 ft long. The glass tubes were connect to a common (mercury) reservoir at the bottom, and 4 pieces of vacuum tubing connected to the tops of the tubes. Looked like a set of overgrown thermometers. Adjust the carbs until the "temperature" was equal on each, and you were golden.

      Had to be careful about making any sudden throttle changes though. Letting the throttle snap shut at higher rpms would create enough vacuum to suck the mercury right out of the tops of the tubes!

      The gauge sets are much more user friendly.


      • #4
        I like the gauge sets. The mercury ones are great too but sadly not available anymore, they have been replaced by steel rods in tubes. I would have gladly taken the mercury ones off your hands.

        As above the gauge sets need a restrictor valve to avoid violent fluctuations that will eventually break them (and to make them possible to read accurately). The orifice need only be small, less than a mm. Cheaper sets use four fish-tank valves and more expensive ones have a needle valve built into each hose barb fitting.
        Peter - novice home machinist, modern motorcycle enthusiast.

        Denford Viceroy 280 Synchro (11 x 24)
        Herbert 0V adapted to R8 by 'Sir John'.
        Monarch 10EE 1942


        • #5
          I never had one of those devices, gauges or mercury, when I needed one for a 3 cylinder Suzuki so I used the rev drop method. I just adjusted the throttle stop for a brisk speed, 1200 rpm or so, then shorted out each plug in turn and the one with the most rev drop I closed a little until they were all even. It was a very good result.


          • #6
            Thanks for the input, the gauges i picked up have a very small opening and are bellow type, perhaps that will offer some dampening. I'll hook one of them up and see what it looks like. They are just the gauge and bezel, no case, so they will need enclosed in something tp protect them.



            • #7
              The only thing I'll add is that they should have an easily accessible calibration screw...if the carbs or TB's are close by previous adjustment or other means, then common manifold them to one carb/TB and calibrate all the guages so they read the same. Then connect the individual carbs/TB's to their respective guages and adjust for synchronization.