Balancing Carburettors

The following explanation was provided by Richard H. Kuschel on the Jag-Lovers E-Type Mailing list on September 17, 2001, and is based on how to operate the UniSyn carburettor air flow meter:

  • Start the engine.
  • Place the device (UniSyn carburettor air flow meter) over the air intake on the first carburettor making sure that there are no air leaks.
  • Change the plate height of the device until the ball floats in the middle of the transparent tube, between the lines.
  • Place the device on the second carb.
  • If the ball is too high unscrew the idle adjustment screw to reduce idle speed until the ball drops to the correct height.
  • If the ball is too low, increase idle speed with the screw.
  • Repeat the procedure until both carbs read the same. You may need to adjust the flow plate on the Unisyn as the engine speed changes due to carb adjustment, but remember that you are trying to balance the carbs relative to one another rather than to some set formula.
  • Once you get the flows balanced and the mixtures correct, check the flow again. You will probably have to increase or decrease idle speed on all carbs to get the final idle speed correct.
  • Recheck flow rates after final setting of idle speed and mixture. It is useful to occasionally blip the throttle after checking the flow on each carb as the Unisyn tends to make the mixture rich and can lead to false readings.
  • If you are doing this on a system with triple SU's, the procedure is the same, you just have increased the amount of time necessary to do this by about double.