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Jabiru Aircraft
Pty Ltd
Instruction & Maintenance Manual
Jabiru 2200 Aircraft Engine
Hydraulic Valve Lifter Models
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REVISION
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Dated : June 2010
Issued By: DPS
Page: 62 of 116
L:\files\Manuals_For_Products\Engine_Manuals\Transition\JEM2204-9_I&M_unsigned.docx
The float chamber (44) is secured to the carburettor housing by a spring yoke (45). A seal
(46) is provided between float chamber and carburettor housing. The space above the
fuel level is connected to atmosphere by two ducts. When these ducts are blocked, an air
cushion forms above the fuel. The fuel will not lift the float sufficiently to close the needle
valve and the carburettor overflows.
The float chamber (44) incorporates an overflow pipe to allow fuel to drain off if the
specified level in the float chamber is exceeded substantially due to a leaking needle
valve.
MAIN REGULATING SYSTEM WITH PRESSURE REGULATOR
The amount of mixture drawn in by the engine and thus its performance is determined by
the cross-sectional area in the choke tube which is opened by the throttle valve (23). The
throttle valve is secured to the valve shaft (24) by two screws (25). The end projecting
from the carburettor housing carries the throttle levers (27) + (28) which are secured by
the nut (3) and washer (29) to which the Bowden cable operating the throttle shaft is
attached. The sealing ring (26) provides the seal between valve shaft and housing. The
retaining arm (31) attached to the carburettor housing by means of screws (32) and
washers (33) engages the notch in the valve shaft and thus prevents it from moving in
axial direction. The return spring (35) whose action opposes the Bowden cable is
attached between a bent-over tab at the lower end of the retaining arm and the throttle
lever (28). If the throttle valve (23) is opened while the engine is running, the increased air
flow in the choke tube results in a vacuum building up at the outlet of the needle jet (3)
which draws fuel from the float chamber through the jet system. At low speeds and in
particular in the case of four-stroke engines, this vacuum is not sufficient for an adequate
fuel supply; it must therefore be increased artificially by using a pressure regulator. For
this purpose the BING constant depression carburettor type 94 is provided with a plunger
(13) operating in conjunction with a diaphragm (16); which reduces the cross-sectional
area or the needle jet outlet by virtue of its own weight or, in some applications with the
additional pressure from a spring (22), and thus increases air velocity and vacuum at this
point.
The plunger (13) is located centrally in the cover (20) which is secured to the carburettor
housing by screws (21). The diaphragm (16) is connected to the plunger (13) by a
retaining ring (17) and four screws (18) and washers (19) each. The vacuum in the choke
tube acts on the top of the diaphragm and the plunger via a bore (U) in the plunger (13)
and attempts to lift the plunger against its own weight and spring (22). The considerably
lower vacuum between air filter and carburettor is applied to the underside of the
diaphragm via duct (V) as a reference pressure.
If the throttle valve (23) is opened when the plunger (13) is closed, then a vacuum will
build up in the small cross-section at the bottom of the plunger (13) which is sufficient to
provide a supply of fuel. The weight of the plunger (13) and the force of the spring (22)
are matched in such a way that this vacuum will be maintained with increasing speed until
the plunger has fully opened the carburettor cross-section. From this point onwards the
carburettor acts as a throttle valve carburettor with fixed choke tube. The vacuum
increases with increasing speed.