BING 40mm carburetors

Balancing 2 BING 40mm carburetors on a BMW flat twin in 3 steps using the TwinMax carburetor synchronizer

Adjust idle speed

1. Warm up the engine for a good 20 km if starting from cold, less if the engine is warm.
2. Use a screwdriver to adjust the idle richness screw carb by carb.
3. Disconnect the right-hand spark plug wire and plug in a spare spark plug, the base of which should be connected to the engine/chassis earth (to avoid shattering the high-voltage coils).
4. Go to the left-hand side of the bike and start the engine, which should still be at operating temperature.
5. Turn the idle richness screw "in" then "out" slowly, until you feel the idle speed stabilize, and listen to the engine.
6. When maximum engine speed is reached for the cylinder being adjusted, turn back 1/8 turn (unscrew).
7. With perfect richness on the left-hand side, stop the engine (turn off the ignition key to avoid snapping the HT coils).
8. Repeat the same procedure on the right-hand side of the motor.
9. If the richness is perfect on the right, stop the motor (turn off the ignition with the key to avoid snapping the HV coils).
10. Reconnect the HV cables to the motor coils.

Setting the idle synchronisation

1. Unscrew the vacuum screws located under the 2 carburetors (Bing CV 40mm for me).
2. Connect the Twinmax's two tubes to the inlets previously plugged by the two vacuum screws
3. Switch on the Twinmax and set the needle offset to "0" using the two buttons on the casing (button 1: offset / button 2: sensitivity). As the result of this step determines all subsequent settings, the needle must be centered at "0" (motor off) and the instrument sensitivity at max.
4. Start the engine (which should still be at operating T°) and bring the instrument sensitivity to 3/4 of maximum (sufficient for good settings).
5. With the idle speed set, the needle should move more or less to the right or left.
6. Select ONE carburetor and adjust the idle speed screw to bring the engine speed up to around 800-900 rpm, even if this further upsets the synchronization.
7. Act on the second carburetor and adjust its idle screw to bring the Twinmax needle to "0". The needle moves a little with the engine's pulsations - this is normal and makes the first attempts at synchronization adjustment a little difficult.
8. If at the end of the idle synchronization the engine speed has stabilized at around 800rpm (not less!) then you've arrived!
9. If not, go back to step 6 and raise the engine speed A LITTLE. This will obviously upset your timing, but by acting on the second carburetor you'll get back to the ideal setting from step 8.
10. Turn off the ignition with the key (to avoid snapping the HT coils).
11. If you don't plan to perform dynamic synchronization afterwards,
12. DON'T FORGET to tighten the carburettor vacuum screws!

Set dynamic synchronization.

1. Unscrew the vacuum screws located under the 2 carburetors (Bing CV 40mm for me).
2. Connect the Twinmax's two tubes to the inlets previously plugged by the two vacuum screws
3. Switch on the Twinmax and set the needle offset to "0" using the two buttons on the casing (button 1: offset / button 2: sensitivity). As the result of this step determines all subsequent settings, the needle must be centered at "0" (motor off) and the instrument sensitivity at max.
4. Start the engine (which should still be at its operating T°C) and bring the instrument sensitivity to 3/4 of maximum (sufficient for good settings).
5. Now that idle speed has been established, the needle MUST NOT deviate to the right or left, as you have just performed idle speed synchronization!
6. At the stop on both carburetors, touch the throttle cables and find out which one is tighter.
7. Enlist the help of a third party, who will accelerate slightly for you up to 1500 rpm (that's enough!), to tighten the 2 throttle cables a little.
8. Using a pair of pliers, adjust the tension of the most taut cable (loosen the tension a little) until the Twinmax needle is perfectly aligned with "0".
9. Switch off the ignition with the key (to avoid snapping the HV coils).
10. DON'T FORGET to tighten the carburettor vacuum screws!

Article written by "Reiler" (thanks to him). Feel free to visit the forum, it's a real goldmine http://www.flat-twin-bmw.com/