TwinMax I Carburetor Synchronizer

Yamaha Bulldog

Yamaha Bulldog

Thanks to françois for kindly writing this tutorial using his own Yamaha Bulldog!


The tooling required is limited to :

  • A set of BTR keys.
  • A flat-nosed pliers for extracting clamps, hoses and plugs.
  • A Twinmax vacuum gauge

Attention, to make this adjustment, the air filter must be clean (or new is better), the spark plugs must be new and adjusted identically with the correct gap.

01 Bring the engine to its normal operating temperature by driving a few kilometers
02  Stop the engine, stand in a ventilated area.
Remove the right and left covers (see photos below).

04  Connect the TwinMax vacuum gauge to the inlet pipes (see photos below).

Switch on the vacuum gauge with the red button after connecting it to the vacuum sockets.
With the motor at a standstill, turn the "sensitivity" knob to half the max. value.
Set the pointer of the meter to "zero" by means of the "zero" button.
Slightly lower the sensitivity.
Start the engine and let it idle, then, bring the engine speed up to 3000 rpm and keep the throttle lever at this speed.
10  Adjust the synchronisation of the carburettors by acting on the screw shown in the photos above, making sure that the needle of the vu-meter is positioned at "zero".

Repeat the same operation, bringing the engine speed up to 5000 rpm (adjust slightly if a small imbalance remains).
Release the throttle and check that, at idle, the needle of the vu-meter oscillates well around the "zero" central point.
You can start again with the vacuum gauge set to the maximum sensitivity.

Once the adjustments are complete, disconnect the TwinMax and replace the cap, hose and flange.