Carburetor Synchronization For smooth idling, synchronization of the throttle valves is  necessary. When synchronizing, slacken both Bowden cables,  and detach the resonator hose (3) of the compensating tube  (2) to separate the two air intake systems.  [Figure 11-26]  In  this condition, no significant difference in the engine running  should be noticeable. If adjustment is needed for synchronous  basic throttle adjustments (mechanical synchronization),  proceed as follows.  [Figures 11-27  and  11-28]  Adjust the two Bowden cables for simultaneous opening  of the throttle valves. Remove the cable fixation (4) on the  throttle lever (1). Next, release the return spring (5) from its  attachment on the throttle lever (1), and return the throttle  lever (1) to its idle stop position (3) by hand. There should be  no resistance during this procedure. Unscrew the idle speed  adjustment screw (2) until it is free of the stop. Insert a 0.1  mm (0.004 in) feeler gauge (gap X) between the idle speed  adjustment screw (2) and the carburetor idle stop (3), then  gently turn the idle screw clockwise until contact is made  with the 0.1 mm (0.004 in) feeler gauge. Pull out the feeler  gauge and turn each idle speed adjustment screw (2) 1.5 turns in clockwise direction. Gently turn each idle mixture screw  (6) clockwise until it is fully inserted and, then, open by 1½  turns counterclockwise. Hook the return spring (5) back up  to the throttle lever (1) in its original position. Check that  the throttle valve opens fully, automatically. Carry out the  above procedure on both carburetors. NOTE: The mechanical carburetor synchronization is  sufficiently exact. At this point, place the throttle lever in the flightdeck to the  idle stop position. Ensure that the throttle lever remains in  this position during the next steps of the synchronization  process. With the throttle lever in the idle stop position,  move the throttle lever (1) to the carburetor idle stop position,  using the cable fixation (4), and secure the Bowden cable  accordingly. As soon as the two carburetor Bowden cables  are installed (throttle lever idle position), check that the idle  speed adjustment screw (2) rests fully on the idle stop (3)  without pressure. 2 3 6 7 7 6 CODE 2 3 6 7 Compensating tube Resonator hose Hex screw Intake manifold X 3 5 7 2 1 4 CODE 1 2 3 Throttle lever Adjustment screw Carburetor idle stop 4 Cable fixation Return spring Idle adjustment 5 7 6 8 CODE 6 8 Mixture screw Mixture screw Figure 11-28.  Idle mixture screw. Figure 11-26.  Resonator hose and compensating tube. Figure 11-27.  Carburetor throttle lever. 11-18