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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: 63 of 116
L:\files\Manuals_For_Products\Engine_Manuals\Transition\JEM2204-9_I&M_unsigned.docx
The space in the cover (20) above the plunger guide is vented through bore (D). Its
diameter is designed in such a way that it acts as a restrictor for air flowing in and out and
therefore acts as a vibration damper for the plunger.
On its way from the float chamber to the choke tube the fuel passes through the main jet
(1), the jet carrier (10) and the needle jet (3); as it leaves the needle jet it is pre-mixed with
air which is brought in from the air filter via an air duct (Z) and the atomiser (2) in an
annular flow around the needle jet. This air flow assists the atomising process to form
minute fuel droplets and thus favourably affects the fuel distribution in the intake manifold
and combustion in the engine.
The conical section of the jet needle (4) which is secured to the plunger (13) with the
retaining spring (14) and the serrated washer (15) engages into the needle jet (3).
Depending on the dimension of the flat cone at the end of the jet needle, the annular gap
between jet needle and needle jet is enlarged or decreased and thus the fuel supply is
throttled to a lesser or greater extent. The jet needle (4) can be located in the plunger (13)
in four different positions which, similarly to the jet needle cone, affect the amount of fuel
drawn in. For example "needle position 3" means that the jet needle has been suspended
from the retaining spring (14) with the third notch from the top. To achieve the height
adjustment the jet needle is turned through 90o and pushed up or down, the retaining
spring engaging the next notch in the jet needle. If the needle is suspended higher up,
this will result in a richer mixture and vice versa.
In short the main regulating system is set using main jets and needle jets of various
diameters and also jet needles, plungers and pistons of various types.
Between main jet (1) and nozzle stock (10) a washer (12) is provided which, together with
the float chamber, forms an annular gap. In particularly severe operating conditions this
ensures that the fuel is not spun away from the main jet.
A rubber ring (11) seals the nozzle stock (10 off from the carburettor housing to avoid any
fuel being drawn in via the thread and thus bypassing the main jet.
IDLING SYSTEM
During idling and low-load running the throttle valve (23) is closed to such an extent that
the air flow underneath the plunger (13) no longer forms a sufficient vacuum. The fuel is
then supplied via an auxiliary system, the idling system, which consists of the idling jet (5),
the idling air jet (LLD) - no spare part - and the mixture control screw (7) which is sealed
off against the carburettor housing by the rubber ring (9) and secured by spring (8) to
prevent it from becoming slack. The fuel passes through the idling jet (5) whose bore will
determine the amount of fuel. Behind the jet bore the fuel mixes with air which is supplied
via cross ducts in the jet throat from the idling air channel, the amount of air admitted
being determined by the size of the idling air jet at the inlet of this duct. This initial mixture
then flows through the idling outlet bore (LA), the cross-sectional area of which can be
adjusted by the mixture control screw (7); it then reaches the choke tube via bypass or
transition passages (BP) where it is mixed further with pure air.