TwinMax I Carburetor Synchronizer



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Bertrand wrote a little tutorial on balancing the carbs of old English motorcycles ... Thanks to him


We assume that your carbs are in good condition, (needle, bushel without abnormal wear, etc.), and that the settings are correct. The ignition has been correctly set before.

Under these conditions, for the synchronization adjustment itself, there remain 2 parameters to be tweaked :

  • The adjustment of the idle screws which allows the opening of the valve to be set to idle, the control cable released.
  • The adjustment of the pulling of the cables (lifting of the bushings or opening of the valves) between 2000 and 3000 rpm for example.


The engine is stopped after having been warmed up. Connect your TwinMax to the intake pipes :

  • On Italians motorbikes (Guzzi, Laverda...), there are holes provided on each intake pipe. You just have to buy the small adapters (M5 or M6) proposed with the TwinMax ... or make them by drilling screws and by welding with tin and soldering iron a small tube of the right diameter.
  • On the Commando ... easy ! Disconnect the small pipe between the pipes and connect the TwinMax hoses instead. Even the diameter is the right one. One more reason to ride Norton !
  • On the Bonneville and Trident, the noble solution is to fit small tubes on each intake pipe and reseal after use with a small rubber stopper. Important! The length of the 2 hoses must remain the same, otherwise it falsifies the setting ! Vacuum sockets must be at the same level on each intake pipe.
  1. Once the TwinMax is connected, it must be powered by pressing the RED button.
  2. With the engine still stopped, turn the SENSITIVITY knob to MAX.
  3. Move the dial hand to zero using the ZERO button.
  4. Decrease sensitivity slightly.
  5. Start the engine and let it idle.
  6. Adjust the idle speed by acting on the idle screws of the 2 carbs so that the Twinmax needle remains at zero.


Once your idle screws are properly adjusted, you need to adjust the balanced pull of the cables.

  1. Bring the speed to 3000 rpm and lock the throttle grip.
  2. By acting on ONE of the two carbs, play on setting the gas cable after loosening its lock nut, so that the twinMax needle remains at zero.
  3. Tighten the lock nut (be careful, it can vary the setting slightly).
  4. Release the gas handle

It's finish! And enough most of the time.


We can start again with the TwinMax set to its maximum sensitivity, but that may not be possible because our old carbs are sometimes a little unstable, especially in slow motion. It works like this ... But I know you'll try !

Remember that the engine is hot, that it does not like it and that if it is too hot, the idle will not be good at its normal temperature.

With a little habit, it only takes a few minutes.