Engine operation generates a vacuum in the intake manifolds, which then draw in an air + gasoline mixture supplied by a carburetor or fuel injection system. The suction power is controlled by a throttle device (valve, butterfly, etc.) connected to the throttle.
Ensuring that each cylinder is supplied with a balanced mixture of air and fuel at all operating speeds makes for a smoother, more efficient engine, and reduces 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 vacuum source. The difference in vacuum is detected by the and presented visually on a dial whose needle oscillates around 0. If one carburetor opens more than the other, this will cause the needle to move towards the tube attached to it.
Preparing for synchronization
On the BMW RT, the nipples used to attach the fuel vapour recovery hoses provide an ideal location for connecting the TwinMax tubes.
Before starting synchronization, with the engine off, the tubes attached to their respective carburetors and the TwinMax switched on, the needle on the display should be set to 0 with the highest possible sensitivity setting, in order to obtain the most accurate calibration.
During synchronization, with the engine running, the needle will oscillate as the intake valves open and close, depending on engine speed. The most effective sensitivity setting to use is around 3/4 turn.
Please note that synchronization takes place with the engine running. Avoid performing this operation in a closed garage, as you may be affected by exhaust fumes.
Normally, the right and left panels must be removed to access the carburettors and connect the Twinmax pipes. However, the left panel can remain in place if synchronization is not required at idle.
Synchronizing the BMW R1100RT or R1150RT is a two-step process: Synchronization is first carried out at idle engine speed, then at the various intermediate engine speeds.
Traditionally, dynamic tuning is performed at 4000 rpm. However, some believe that 2500 rpm, or the rpm reached when both gas pedals are just open, produces the same, or very similar, results. If you wish to travel at a given speed, note the engine speed most used at that speed and synchronize to it. This will minimize vibration at your preferred cruising speed.
- Twinmax with new battery
- Sized tubes for throttle body suction ports
- Slotted screwdriver
- 3 mm Allen key
- 10mm open-end wrench
- Needle-nose pliers.
Preparing for synchronization
- Bring the engine up to normal operating temperature
- Switch off the hot engine and place the motorcycle on its center stand.
- Remove the left and right panels.
- Remove the rubber vapor recovery tubes from the lower side of each throttle body.
- Place the Twinmax on the saddle so that you can see the dial.
- Insert the Twinmax hoses into the timing sockets on side A to the left and side B to the right.
Synchronization at idle is achieved by adjusting the low-profile brass adjusting screws, leaving each throttle cable about 1 cm of play.
At idle, the fuel injectors deliver a constant quantity of fuel to each cylinder, under the control of the throttle position sensor (TPS).
Adjustment of the air adjusting screw modifies the amount of air allowed to pass to the idle circuit:
Adjusting these screws has two effects: the air/fuel mixture at idle is modified, and the idle speed is altered.
Synchronization must be achieved within a range of 1000rpm, +/- 50rpm. If synchronization cannot be achieved, in most cases the TPS parameter must be modified. In this case, it is advisable to contact a competent BMW dealer.
Engine idle synchronization
- Loosen the right-hand cable adjustment locknut, as this is where you will adjust the throttle in step 2. Do not loosen and adjust the left-hand throttle cable, as this will interfere with the TPS adjustment.
- Switch on the Twinmax.
- Turn the "Sensitivities" knob clockwise to "Maxi".
- Adjust the "Zero" knob until the dial needle is precisely in the middle of zero on the scale. This adjustment is very sensitive and very important.
- Turn the "Sensitivity" knob counter-clockwise to "Mini".
- Start the engine and let it idle.
- Slowly turn the "Sensitivity" knob until a deviation is displayed on the scale.
- Adjust the idle screw(s) on the throttle body until the display shows zero. The counter is very sensitive, so it's best to proceed in stages, increasing sensitivity each time.
- Leave the engine running and switch to dynamic synchronization.
- If the locknut on the right-hand cable adjuster has not been loosened, do so now.
- Start with the "Sensitivity" knob in the middle of its range.
- Start the engine, gently open the throttle and run the gears up to 3000 or 4000 rpm. The needle will oscillate, the aim being to make it oscillate equally on either side of 0. If the needle movement is not pronounced, increase sensitivity.
- At 2500 rpm, hold the throttle grip and adjust the knurled part on the right-hand side of the throttle body with your other hand. The speedo needle will oscillate. Adjust the cable until you can obtain equal deviation on either side of the zero point. Let the engine return to idle, checking the needle alignment again.
- After dynamic synchronization, tighten the cable adjuster locknut, making sure that the adjuster does not turn with the locknut. This is easier if you hold the knurled adjuster with a pair of pliers while tightening the locknut with a 10 mm wrench.
- Check again that the Twinmax needle is still set to zero at the selected intermediate speeds after tightening the cable locknut, and that no change has occurred.
- Check your idle settings again to make sure they haven't changed. You may need to work through the timing settings for both idle and intermediate speeds to fine-tune the engine.
- If all goes well, switch off the engine, switch off Twinmax and smile, your carburetors are balanced.