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Identification Of Parts And Operation Of Basic Circuits; The Float Circuit; Measuring The Float Level - Ducati 900SS Workshop Manual

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CARBURETOR
Identification of parts, and operation of basic
circuits.
THE FLO
AT
CIRCUIT
The floa
t
circuit is o very
important port
of
the
slide·volve
carburetor.
It must accurately
maintain a specific fuel level
in
the floor bowl or all
times.
The
major components of the
floor circuit
ore the
float bowl
. the float volve-ond·seor
assembly, and the floats. Many
slide·volve
carburetors use
separate.
independ
enl
flools.
and o float arm
thai
connecls
1hem
to 1he
float
vo
lvo.
Because
the
feed tubes
for
the
main.
pilot,
and
storler
circuits
exlend
1nto
the fuel
from
the
main carburetor
body,
the fuel level in the flool
bowl
musl
be
high
enough
to reach
!hem.
But, even
more
significantly,
the
fuel level
actually
affec ts how
rich or
leon the
eng ine
runs
throug
h
its
entire
range
.
The
reason
for
this
goes
bock
to 1he
d
iscussion
o
f
1he
venturi
principle.
parlicularly
1he drop
in
vacuum
1 ho1
occours
in
the
venturi a
l
low
air
speeds.
lithe
fuel level is loo low,
the decreased
vacuum
in
1he venturi
cannel
pull
enough
fuel out
of
the
fuel
bowl and
inlo the
airstream
TIPS:
A
low
fu
el
level causes
hard
starling and
o
lean
ai
r
fuel
mixture at low speeds. Fuel
starvation
may also result
at
high
speeds.
On the
other hand. ,f the
fuel level is too
high.
too
much fuel
is
drown
into
the
ventun,
resulting
1n on overly
nch
mixture
.
M EASURING
TH
E FO AT
LEVEL
This
measurement is
token
from
the
bollom
of the float.
or
the float
lever
on
some
models.
to the
carburetor-body gasket
surface.
. . . NOTE: The float
should
be
resting
on, but not
de pressing, the
spring-loaded
. . . float valve needle.
The float
level
is adjusted by bending
the
tab on the
float
arm.
Bend•ng
the tab
toward
the
needle
valve
raises
the
lloollevel, while
bending
the tab
away
from
I
he
valve lowers
the
floa
t
level.
It
should always be remembered !hot
o
h1gh
float
level
resuhs
in a
low
fuel
level. and o
lo
w float level
results
in
o high
fuel level.
TIPS:
A fuellevellhot
is
too
low usually shows up
as o leon
condition
It
may hove
o reading
of
low
CO
a nd low·ta·normol HC.
Under
severe
candilions.
this
could
cause
o lean
misfi
re.
In
the
exhausl
gas a
nalyzer
show
s
1hese
readings.
a
nd the
b
ike hesito les
o
ff
idle. you
should
check
the
fuel
level This is
especially importonl
on
models
equipped wiih
CV
corburelors.
The lower
the
fuel level. the
more
resistance
the
fuel
hos
to being
drown
into the venturi
.
This is
whol
causes leon
readings on
the
exhousl
gos
analyzer.
A
fuel
level thai
is
too
high
normally
sho
ws
up
a
s o rich reading
on
the
exhaust
gos
analyzer.
Hig
h
CO and
normal-le-high HC
may be your
readings
-
-

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