Jabiru 3300 Instruction And Maintenance Manual Download

Page: 56 / 103

Page No: 56

Issue No: 1

Date: 031100

Issued By: PJA

selected so that foreign bodies greater than 0.1mm are filtered out and the fuel supply is
not impeded to too great an extent.

The float needle (42) contains a spring-loaded plunger which contacts the float hinge.
This absorbs vibrations on the float (40). In addition the float needle (42) is connected to
the float hinge by the retaining spring (43) to prevent it from moving between float and
valve seat and thus reducing the fuel supply. Spring and retaining guide make a
considerable contribution towards keeping the fuel level in the float chamber constant.

When fitting a new float, the fuel level must be adjusted. When doing this care must be
taken to ensure that the fuel needle spring is not compressed by the float weight. It is
therefore advisable to put the carburettor in a horizontal position until the float just
contacts the float needle. In this position the point on the float hinge is set in such a way
that the float top edges are parallel to the top edge of the float chamber.

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 64 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.