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The Pilot Circuit - Ducati 900SS Workshop Manual

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Table of Contents
-
CARBURETOR
The
pilot
circuit.
The
pilot circuit meters the air-fuel
m•xture at idle
and at small
throttle
openings.
The
pilot
circuit
consists
of
a senes
of
passages
in the
carburetor
body, o
pilot jet to
meter
fuel.
and
o
pilot
screw
.
In
some models, the pdo
t
screw
meters
the
air
flow
through
the
pilot
circuit.
This system
is
used o
n the
sl•de-typc
corbu•eto•s
In othe1
models the p•lot
setew controls
the amount
of awfuel mixture
flowing
through
the
pilot circuit.
lhis
version
is
no•mally
found on
CV
carburetors.
. . .
NOTE:
On
some
carburetors the air
jets are located
in
the
top part
of the
. . . carburetor
body,
underneath
the diaphragm.
When cleaning or replacing
them, care should
be take
n that
they are
not
interchanged.
Poor
pe rformance
will
result.
TIPS:
l)A p
1
lo1 circu11thot
1
S
1
00 leon wd1 cause
lower
than
normal
CO
readings and
low-lo-
no
rmol
HC.
If
the
leon
condihon
1
s severe
enough
to
cause
leon
misfire,
the
HC
readings
will
be very
high.
A
machine
w
ith
this condition
will
usua
lly
experience
o
hesllotion
just
off
or
idle.
2)A
pdol
circuit
that
IS
rich
will cause
higher than normal CO readings and normal-to-
high
HC,
depend1ng on how severe the
condition
is.
A machine with this
condition
w1ll g•ve poor
fuel economy
and
.
usually.
poor
performance os well.
Fuel fa• the
pilot
cucu1
t
1
s
drown
thro
ugh the
pilot
jet. which protrudes
into
the
float bowl.
Air
for
the
pilot
circuit
enters
through
o small
passage in
the
inlet
side of the
venturi and,
in
some
models.
is
metered
by
the p
ilot
screw
.
This
screw
is tapered to provide a
g1adual
tncreose
in
a
ir
flow
os the screw
is
backed
out.
MIKUNI uses
two
different
types
of
pdot jets in its
carburetors.
One is the primary type.
wh1ch has only the metering hole
drilled
through its
entire
length.
The other is
lhe
air-bleed type. which has o series
of holes drilled
through
its
sides These
air bleed holes
correspond
wirh
the
pdot
circuit air
passage.
As air flows through
these
holes. the
fuel
bubbles.
ond
becomes
part
ially atomized
before
entering the
venturi
air
stream
c
TIPS:
NOTE:
Although these jets are the
same physical
size, they
should
not
be
interchanged.
lnterchang1
ng
the
pdot
1 e1
s •esulis
•n
p001
pcdo1
rnonce
.
If
the
primary
type is
1 eplaced
with the
air-bleed type
a
very
rich
cond
ition
w ill
exist
at
idle.
0
0
-
@
r
I)
Spurgo
ouo
I
1\or oleeo
•2)
Pnmo11n
l~en70
spurgo
nr•o
t
I
Prrmory
(non-oir
bleed}
0.33

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