TwinMax I Carburetor Synchronizer

BMW R1100RT

BMW R1100RT

THEORY

  • The operation of an engine generates a vacuum in the intake manifolds, which then sucks in an air + petrol mixture supplied by a carburetor or an injection system. The suction power is controlled by a throttle device (ball, throttle valve, etc.) connected to the throttle handle.
  • Ensuring that each cylinder is supplied with a balanced air + petrol mixture, whatever the operating speed, results in a smoother, more efficient engine and reduces the stress on the mechanical assembly.
  • The Twinmax is an electronic pressure sensor that measures and displays the pressure difference (vacuum) between two sources. The two tubes leading to the Twinmax must be connected to a suction source. The difference in vacuum is detected by the and presented visually on a dial whose pointer oscillates around 0. If one carburetor opens more than the other, this will cause the pointer to move towards the tube attached to it.

 

PREPARATION OF SYNCHRONISATION
  • On the BMW RT, the end caps used to attach the petrol vapor recovery hoses provide an ideal location for connecting the TwinMax tubes.
  • Before starting the synchronisation, engine off, hoses attached to their respective carburetors, TwinMax on, the needle of the display must be set to 0 with the highest possible sensitivity setting in order to obtain the most accurate calibration.
  • During synchronisation, with the engine running, the needle will oscillate with the opening and closing of the intake valves depending on the engine speed. The most effective sensitivity setting to use is then approximately 3/4 turn.
  • Caution, the synchronisation is carried out with the motor running. Avoid carrying out this operation in a closed garage, you could be bothered by exhaust fumes.

SYNCHRONIZATION PROCESS
  • Normally, the right and left panels must be removed to access the carburetors and connect the Twinmax hoses. However, the left panel can remain in place if it is not necessary to synchronise at idle.
  • The synchronisation of the BMW R1100RT or R1150RT is a two-step process: Synchronisation is first carried out at idling engine speed and then at various intermediate engine speeds.
  • Traditionally, dynamic adjustment is carried out at 4000 rpm. However, some estimate that 2500 rpm, or the rpm reached when both accelerators are just open, produces the same or very similar results. If you want to travel at a given speed, note the engine speed most used at that speed and synchronise to that speed. This will minimise vibration at your preferred cruising speed.

TOOLS
  • Twinmax with a new battery
  • Tubes dimensioned for the suction ports of the throttle body
  • Slotted screwdriver
  • 3 mm spanner
  • 10mm spanner
  • Needle nose pliers.
PREPARATION OF SYNCHRONISATION
01
Bring the engine to its normal operating temperature.
02
Turn off the engine while it is still warm and place the motorbike on its central stand.
03
Remove the left and right panels.
04
Remove the rubber vapor recovery tubes from the underside of each throttle body.
05
Place the Twinmax on the saddle so that you can visualise the dial.
06 Insert the Twinmax hoses into the synchronisation sockets on side A to the left and on side B to the right.

Synchronisation at idle is achieved by adjusting the low brass adjustment screws, leaving a clearance of about 1cm for each acceleration cable.
At idle, the fuel injectors deliver a constant amount of fuel to each cylinder under the control of the Throttle Position Sensor (TPS).
Adjusting the air adjusting screw changes the amount of air allowed to pass to the idle circuit:
Adjusting these screws has two effects: the air/fuel mixture at idle is changed and the idle speed is altered.
Synchronisation should be performed within a range of 1000rpm, +/- 50rpm. If synchronisation cannot be achieved, most of the time the TPS parameter must be changed. In this case, it is advisable to contact a competent BMW dealer.
 
IDLE SYNCHRONISATION
01
Loosen the locknut on the right cable adjuster, as this is where you will make the throttle adjustment in step 2. Do not loosen and adjust the cable on the left gas side as this will interfere with the TPS adjustment.
02
Switch on the Twinmax.
03
Turn the "Sensitivities" knob to "Maxi" in a clockwise direction.
04
Adjust the "Zero" button until the dial hand is precisely in the middle of zero on the scale. This adjustment is very sensitive and very important.
05
Turn the "Sensitivity" knob to "Mini" counterclockwise.
06
Start the engine and let it idle.
07
Slowly turn the "Sensitivity" knob until a deviation is displayed on the scale.
08
Adjust the idle screw(s) on the throttle body until the display reads zero. The speedometer is very sensitive, so it is advisable to proceed in stages, increasing the sensitivity each time.
09  Leave the motor running and switch to dynamic synchronisation.

DYNAMIC SYNCHRONISATION
01
If the lock nut on the right cable adjuster has not been loosened, do it now.
02
Start with the "Sensitivity" button in the middle of its range.
03
Start the engine, open the throttle slowly and execute speeds up to 3000 or 4000 rpm. The needle will oscillate, the aim is to make it oscillate equally on each side of 0. If the needle movement is not pronounced, increase the sensitivity.
04
At 2500 rpm, hold the throttle grip and adjust the knurled part on the right side of the throttle body with your other hand. The meter needle will oscillate. Adjust the cable until you can achieve equal deflection on either side of the zero point. Allow the engine to idle and check the needle alignment again.
05
After dynamic synchronisation, tighten the locknut of the cable adjustment, making sure that the adjustment does not rotate with the locknut. This is easier if you hold the knurled adjuster with pliers while you tighten the locknut with a 10 mm spanner.
06
Check again that the needle of the Twinmax is still set to zero at the selected intermediate speeds after tightening the rope locknut and that no changes have taken place.
08
Check your idle settings again to make sure they have not changed. You may need to work through the timing settings for idle as well as intermediate speeds to fine-tune the engine.
08  If all goes well, switch off the engine, switch off Twinmax and smile, your carburetors are balanced.

Article written by Bill Hawkins with contributions from G. McCurdy, Dick Frantz & Lee Sayers