Rotax 912-UL Repair Manual

For
this
purpose
the BING
constant
depression carburetor
type 64
is provided
with
a
plunger
(19)
operating in
conjunction
with
a
diaphragm
(23)
which reduces
the
cross-sectional
area
or the
needle
jet
outlet by
virnre
of its
own weight or, in
some
application
with
the additional
pressure
from
a spring
(26),
and thus increases
air
velocity
and
vacuum
at
this
point.
The
plunger
(19)
is located
cenrally
in
the cover
(27)
which is
secured
to the
carburetorhousing
byscrews
(28).
The
diaphragm
(23)
is
connected to
the
plunger
(19)
by a retaining ring
(24)
and
fourscrews
(25)
and washers. The vacuum
in the
choke
tube acts on
the top
of
the diaphragm
and
the
plunger
via a bore
(U)
in
the
plunger
(19)
and
attempts to
lift
the
plunger
against
its
own weight
and spring
(26).
The
considerably lower vacuum
between air filter
and carburetor is
applied
to the
underside
of
the diaphragm via duct
(V)
as a reference
pressure.
If
the
throttle valve
(41)
is
opened when the
plunger
(19)
is
closed, then
a
vacuum
will
build
up
in
the small cross section
at the bottom of the
plunger
(19)
which is
sufficient
to
provide
a
supply
of
fuel. The
weight
of the
plunger
(19)
and
the force
of
the spring
(26)
are
matchedin
suchaway thatthisvacuum will
be maintained
with
increasing
speed
until the
plunger
has fully
opened
the
carburetor
cross-section.
From
this
point
onwards
the carburetor acts
as a throttle valve carburetorwith
frxed
choke
tube. The vacuum increases
with increasing
speed. The
space in
the cover
(27)
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
(7),
the
jet
carrier
(5)
and the
needle
jet
(3),
and
as
it leaves
the needle
jet
it
is
pre-mixed
with airwhich
is
brought
in
from
the airfiltervia
an air duct
(Z)
and
the
atomizer.
(2)
in.an
annular
flow around the
needle
jet.
This
air flow
assists
the
atomizinS'frocess
to
form
minute fuel
distribution in
the
intake
manifold
and
combustion in
the engine.
The
jet
needle
(20)
is secured
to the
plunger
(19)
by the
retaining
clip
(2f)
and
holding nut
(22\.The
conical
portbn
of the
jet
needle
engages
into
the
needle
jet
(3)
and,
depertding on cone
dze of the
jet
needle,
the annular
area between
needle
f0jet
is
enlarged or reduced,
thus
throaling
the fuel suAll more
or
less. The
jet
needle
(20)
can be set in
the
plunger
(19)
to four
different
positions,
which similarly
to the cone affect
the
quantity
of
fuel
drawn
in.
To
change
needle
position,
remove
holding
nut
(22)
and shift
retaining
clip either up or
down to next notch.
The
higher
the needle,
the
richer the
mixture
and
vice
versa
needle
posltlon
-1
-2
-3
-4
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Rotax 912-UL Specifications

General

Displacement	1211 cc
Bore x Stroke	79.5 mm x 61 mm
Compression Ratio	9.0:1
TBO (Time Between Overhaul)	2000 hours
Engine Type	4-cylinder, 4-stroke
Power Output	80 hp
Cooling System	Liquid/air-cooled
Fuel Type	Avgas 100LL or unleaded automotive gasoline
Oil Capacity	3 liters
Fuel System	2 carburetors
Oil System	Dry sump forced lubrication with separate oil tank
Reduction Gear Ratio	2.43:1
Max Continuous Power	75 hp (56 kW)