Rotax 912-UL - 4> Main Regulating System with Pressure Control

'
In
addition, the
float needle
(10)
is
connected
to the
float hinge
by the
retaining
spring
(11)
topreventit
from
movingbetween
floatand valve
seatand thusreducing
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 carburetor
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.
I
The float
chamber
(15)
is
secured to the
carburetor housing by a spring
yoke
(18).
A
gasket
(17)
is
provided
between
float chamber and carburetor 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
carburetor overflows.
The float
chamber
(15)
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.
7.15.4) 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
(a1).
The
throttle
valve is
secured to the
valve shaft
(39)
by
two
screws
(42).
The
end
projecting
from
the carburetor
housing carries
the
throttle
levers
(a6)
and
(a7)
which
are
secured
by the
nut
(37)
and
washer
(36)
to which the Bowden
cable
operating
the throttle shaft
is
attached.
The
sealing
ring
(40)
provides
the seal between
valve
shaft and housing. The
retaining
arm
(43)
attached to the carburetor
housing
by means of
screws
(44)
and
washers
engages
in
the
notch in
the
valve shaft
and thus
prevents
it from
moving
in
axial
direction.
The return
spring
(48)
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
(47).
If the
throttle
valve
(41)
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.