Synchronisation d'une Honda Transalp avec le dépressiomètre TwinMax

Honda Transalp

The website is a reference site for all Honda Transalp owners. You will find tons of useful information and also a tutorial on carburettor synchronisation using the TwinMax.


This operation should be performed with the engine at its optimum operating temperature.

The valve clearance must have been adjusted beforehand (cold engine, the air filter must be clean (see new), the spark plugs must be "clean" (see new), the carburetors must have been adjusted

The material required is as follows 

  • 8, 10 and 12mm spanners or sockets
  • Phillips screwdriver size 2
  • Flat screwdriver
  • Lamp or other lighting
  • Twinmax pressure gauge

Preliminary disassemblies

  • The speedometer cover (4 crosshead screws)
  • Front side panels (2 cross head screws)
  • The rear side panels (1 x 10 mm screw per side panel)
  • The seat (2 x 10 mm screws)
  • The tank (1 x 12 mm screw)

Some theory about carburetors balancing.

The vacuum reference value is set by the left carburetor (the one of the rear cylinder). The adjustment screw for the carburetor synchronisation is located between the 2 carburetors

The screw is attached to the left carburetor lifter (blue arrow), which is controlled by the throttle via the throttle cables

The right carburetor lifter (yellow arrow) is attached to the control plate (front cylinder, red arrow and red dotted line)

When the adjusting screw is turned, the right carburettor lever is lowered or raised, which causes the right carburettor valve to be raised or lowered via the control plate (red dotted line)

The vacuum created by the front cylinder acts on the vacuum gauge

The vacuum gauge calculates the difference in vacuum between the 2 cylinders and displays it on the measurement dial

Synchronisation is considered good when the difference in vacuum between the 2 cylinders tends towards zero

Carburetors balancing, how to ?

With the engine running, using a pair of pliers (wooden clothes peg, vice grip, framer's pliers, etc.), clamp the vacuum hose of the fuel valve.

Disconnect the fuel valve vacuum hose from the rear cylinder vacuum port

Leave it running, the engine should not stop. If the engine stops when the carburetors are empty, the clamp has been placed incorrectly, then reconnect the hose and repeat the operation, otherwise stop the engine

Left side of the engine

Unscrew the vacuum connector from the rear cylinder (watch out for the sealing washer)

Screw on the Twinmax connector (2 x 5mm connectors to be ordered at the same time as the Twinmax) Connect the Twinmax "A" socket hose to this connector


Right side of the engine

Use a Phillips screwdriver to remove the vacuum port screw from the front cylinder. (Be careful with the sealing washer)

Screw on the Twinmax end cap in its place

Connect the hose from socket "B" of the Twinmax to this connector

With the engine still stopped, calibrate the Twinmax as follows:

  • Turn it on
  • Set the sensitivity button to "MAX".
  • Use the "ZERO" button to move the needle to the "0" position on the dial
  • Set the sensitivity button back to "MINI".

Move the tank backwards so that there is a clear passage through the air ramp between the carburetors and the airbox

It is through this hole that you will adjust the synchro with a long flat screwdriver

Start the engine and hold it in fast idle using the idle speed control knob (approx. 2500 rpm)

The most difficult part is to put the screwdriver on the adjusting screw: use the lamp to locate it, the rest is a matter of "feeling". Personally I worked from the right side of the bike, it seemed to me better to "see" the adjustment screw

Screw in or out this screw to bring the needle as close as possible to the "Zero" of the dial with a possible equivalent travel on both sides of the zero if the rpm is not high enough

Increase the sensitivity to fine-tune the setting. Sometimes you will need to increase the idle speed.

Do not press on the screwdriver when adjusting, as this will distort the adjustment (the screw is on the "linkage-transmission" between the two carburettors, so when you press you increase the lift of the bushels)

Reduce the idle speed to its optimum position (1300 rpm +/- 100) using the idle speed adjustment wheel

Switch off the engine and carry out the various reassemblies, that's it

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