TwinMax I Carburetor Synchronizer




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Bertrand has written a short tutorial on how to balance the carbs of old English cars using the TwinMax depressiometer... Thanks to him!



We assume that your carburettors are in good condition, (needle, ball without abnormal wear, etc.), and that the float and richness settings are correct. The ignition has been correctly adjusted beforehand.

Under these conditions, for the actual synchronisation adjustment, 2 parameters still need to be fine-tuned:

  1. The adjustment of the idling screws which, as the name suggests, allow you to adjust the opening of the bushel at idle with the control cable slackened.
  2. The adjustment of the cable pull (lifting of the bushes or opening of the throttles) between 2000 and 3000 rpm for example.



The engine is switched off after being warmed up beforehand. All you have to do is connect your TwinMax to the intake manifolds. :

On the Italian ones (Guzzi, Laverda), there are holes on each intake pipe. Simply buy the small fittings offered with the Twinmax...or make them by drilling screws and soldering a small tube of the correct diameter with a tin soldering iron.

On the Commando... easy! Disconnect the small pipe between the pipes and connect the Twinmax pipes instead. Even the diameter is right. All the more reason to ride Norton!

On Bonneville and Trident, the noble solution is to fit small tubes on each intake pipe and to cap them after use with a small rubber stopper. Important! The length of the 2 rubber tubes must remain the same, otherwise the adjustment will be distorted! The vacuum connections must be at the same level on each inlet pipe.

Once the TwinMax is connected, it must be powered by pressing the red button.
With the engine still stopped, turn the "Sensitivity" knob all the way to "Max".
Set the dial hand to zero using the "Zero" button.
Decrease the sensitivity a little.
Start the engine and let it idle.
06 Adjust the idle speed by acting on the idle screws of the 2 carbs so that the needle of the Twinmax remains at zero.


Once your idle screws have been properly adjusted, you will need to adjust the balanced cable pull.

Bring the rpm up to 3000 rpm and lock the throttle.
Acting on only one of the 2 carbs, play on the adjustment of the throttle cable after loosening its locknut, so that the needle of the twinMax remains at zero.
Tighten the locknut (caution, this may cause the adjustment to vary slightly).
Release the throttle
It's over! And sufficient most of the time.
06 Drive !



We can start again with the TwinMax set at its maximum sensitivity, but this may prove impossible because our old carbs are sometimes a bit unstable, especially at idle. It works well like that... But I know you'll try!
Just think that the engine gets hot, that it doesn't like it and that if it's too hot, idling won't be good anymore at its normal temperature.
With a bit of practice, it only takes a few minutes.