Carburator Synchronisation
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Graphic: Synchron tester connected to one carburator each |
Adjusting the idle speed at BING-constant depression carburator Typ 64-32
1. Study the functional description of the carburetor. Observe the engine manufacturer's special setting guidelines. Familiarize yourself with your synchroniser tester. All instructions relating to one carburetor also apply to the other. When overhauling the carburetor (or if it has been completely set incorrectly), in addition to other "internal" settings (e.g. float level, jet needle suspended in the correct notch), the "external" throttle valve, the bowden cable and the idle mixture screw must also be adjusted (with the carburetor removed or the engine at rest). The throttle valve and idle mixture initial settings can be omitted at the maintenance idle adjustment.
Initial throttle valve setting: Close the throttle valve completely (loosen the bowden cable, turn back the stop screw, move the spiral spring so that the valve is completely closed). Then screw in the throttle stop screw until it touches the throttle lever but does not yet open. From now on, screw in the stop screw further until the valve is minimally "forced open". Follow the engine manufacturer's instructions (feeler gauge 0.1 mm + 1.5 turns). Hang the spiral spring back again. Carry out initial bowden cable adjustment.
Initial bowden cable adjustment: fix the loosened bowden cable so that the throttle valve lever is just at the stop screw at idle position; when the throttle lever is pulled, both throttle valves must then open synchronously. Carry out initial idle mixture adjustment.
Initial idle mixture setting: Screw in the idle mixture screw fully and unscrew it according to the engine manufacturer's specifications (1.5 turns).
2. Secure the aircraft well against rolling away, even in the unlikely event that the engine roars unintentionally.
3. Prepare the vacuum tapping points (hereinafter referred to as hose nozzle). Screw the hose nozzle into the intake manifold (M6) or, if not available, remove the compensation tube and fit the hose nozzle to it. To simplify subsequent adjustments, the hose nozzle can be permanently installed in the intake manifold. For normal operation, however, it must be possible to close it permanently and securely and it must not affect the carburettor function in any way (e.g. hose nozzle with internal grub screw + cap)!
4. Connect the hose ends of the pressure gauges to the both open hose nozzles. Close the pressure gauge dampers first because otherwise the pressure gauges would be damaged by the violent pulsation of the intake strokes. If the compensation tube still connects the carburetors, close it so that the carburetors can be measured in isolation from each other. Here, too, you could permanently install a shut-off valve that can be easily opened again later.
5. Start the engine, oil temperature at least 50°C - pull to idle, rehang the throttle valve spiral spring (now closes the throttle valve) and loosen the bowden cables. Carefully open the pressure gauge dampers until the hands do not swings too violently and the average value can be read.
6. The pressure gauges (average values of the trembling hands) should be the same on both sides.
Adjust the throttle valve using the stop screw, taking into account the idling speed
recommended by the engine manufacturer of 1600 rpm:
If the idling speed is too high, close the
throttle valve slightly (unscrew the stop screw). Start with the carburetor
with the lower vacuum (-0.4 is lower than -0.5). It may be necessary to make
several adjustments, also alternating on the carburetor side. If the engine
speed is too low, proceed in reverse. The aim is to achieve the required speed
and for both pressure gauges to show almost identical vacuum. This requires
several attempts and patience.
After successful synchronisation, fix the bowden cable (throttle lever in idle
position) again so that it brings the throttle valve to the stop screw when the
throttle lever is in idle position, but does not change the idle speed.
Reposition the spiral spring so that it would open the throttle valve if the bowden
cable were to break. Check the bowden cables again by accelerating the engine speed gently and
fine-tune them if necessary so that the idle setting is maintained and the
vacuum conditions are even. Switch off the running engine and disconnect the
pressure gauge hoses. Close the hose nozzles securely and, if a valve is
installed in the compensation tube, open it.
7. For experienced only, check the idle mixture: With the engine running, achieve the highest possible speed by turning the mixture screws on the already synchronised carburetors. Turn the screw in or out in small steps. Once the screw position has been found, turning it further forwards or backwards would reduce the engine speed again. The best way to optimise the engine speed is with a sensitive digital rev counter. If you are unsuccessful, return the idle mixture screws to the initial setting and leave it at that. If you have been able to optimise the engine speed and it has increased significantly as a result, then reduce it again - back to 2.
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