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i
Carburetor
malfun
ctionin g can also
be cause d by worn
parts . Needle
valv
e
and
seat s
hould
be
che cke d and
replaced as a unit
if
necessar
y.
Needle
valves
should
be
checked
for
grooves
caused
by
overtig hte ning. Seats will
usu ally be damaged
if thi
s is
th
e case.
Needle valve
adjusti ng should
be done
lightl
y to
pr
event needle
and
sea
t
dama ge.
DISASSEMBLY. Refer
to
Fig.
4.
Remo ve retainin g
scre w
(15)
and
fuel
bowl (13). Knock
out
float
pin and
remove float.
Check
float for dents,
leak s
and
wear
on
float
lip or in
float
pin holes. Remove
inlet
needle
(9) and
seat
(8).
Remove idle mixture needle
(21), main fuel
needl
e
(1
)
and springs
.
Note
cond ition
of choke and
throttle
s
ha fts
an
d pl
at e s.
If
we ar e
xis ts,
ca r b ureto r body a
s sembl y
must
be
r
enew ed .
r
1
~
·
L. 3 ~
~
",'"
19
~
l;,r
r
:;-?\
5
11
_
R
~8
18
16~
1).-9
10
~:.;
C
>-12
g-13
15~
-14
Fig. 4-Exploded view of typical Carter
Model
U
N "
carburetor.
I. Main
fuel needl e
2.
Spr-ing
13.
F
loat
bowl
3
.
Car
buretor
body
14. Sea
lin/{ wash er
4.
Choke
s
ha
ft
15.
Retainer
5.
Choke
disc
16.
Main jet
6.
Choke
det ent
17.
Pl
u~
7.
Sea
ling
wash er
18.
Spr ing
8.
Inlet valve seat
19. Idle
sto p scre w
9.
Inlet
va
lve
20. Th
rottl e disc
10.
F
loat
pin
21.
Idle fuel needl e
II.
F
loat
12.
Gasket
~~
:
~h~~~fl e
shaft
ASSEMBLY.
Install
inlet
sea
t and
needle . Install float
and
float
pin. Set
float
level
by
inverting
car bure tor
with
float
r
esting lightly
on inlet
needle.
Measure between
body
gas
ket
flan ge
and float at th
e
point
opposite
th
e
needl e valve . The measurement
should
be
11/64
-in ch
.
Fl
oat a
dj us t me nt is
made by bending t
ang
conta
ct
i
needl e
valve. Install
new
fuel
b:
gask
et,
fu
el
bowl, r
etaining sc
r
gasket (if needed),
and
retaining sen
Install main fuel needle. Install
mixture needle . Do not
overt
igh:
needles
in
sea
ts .
Make
running ad
j
i,
ments.
KEIHIN DIAPHRAGM CARBURETOR
KEIHIN diaphragm type carburetors
are
designed
for snowmobile
use
and.
prior to 1972 produ
ction,
wer
e
available
in two
series;
406 which
is roughly
equivalent in size and appli
cati on
to
Tillots on
HR;
and
407,
equivalent to
Tillolson
RD.
Starti ng with the 1972
model yea
r , a
new method
of
identification was
used
Model
numb
er of
all
carburetors
begins
with prefix
letters "CD," followed by a
numb
er s
uch
as
"33-28."
First part
of
numb
er indicat
es
throttle
bore
(in
milli
met er s)
and
second part
of numb
er
indicates
vent ur i
diamet er
.
OPERATION
F
uel
level
(Main)
diaphragm
(7-
Fig.
5) is below fuel
pump
diaphragm (2).
A
choke shutte r
closes
th
e
carbure tor air
horn to
initiate
th
e
star
ting
mode.
Slow sp
eed oper ation
is controlled
by
settinz of
idle
adiust ment
needle
(l)
and
by
a se
r ies of
drilled dischar ge
ports
(See Fig. 6)
located
below
the
edge of closed
throttle shutter.
Dr illed
ports
(three or four ) ar
e uncovered
Fig.
5-
View of Keihin Diaphragm Carburetor
showing points of
adjustment.
s
equ entially as
thr
ottl e s
hut ter
moved from
idle
position ,
thu
s sUPI
ing
addit ional
fuel for correct mixt
as air
flow
incr
eases. At high s
p«
th
e prim ary venturi
and main
I
di
schar g e nozzl e
ar
e
brou
gh t
i
:
oper at
ion.
s
uppleme nting th
e fuel
wh
conti
nues to
flow
through
th
e
I
discharge ports.
In thi
s manner,
and air are balan
ced throughout
operating
range.
ADJUSTMENT
Carburet ors
ar
e divided
into
eo
and
lat e
typ
es as
out lined in
introo
Fig.
6-
View
of lower surface of cemu«
body showing idle bypass cover
remove,
I.
Gasket
P
.
Puls
e
pa
I. Idle bypass cove
r
X.
Fu
e
l
po
r
t
Fig.
7-
View of lower surface of
cetbu
«
body wi
th
Idle bypass cover (/) and
exp
sian
plug
1M)
installed
.
Refer elsa to Fig
.
A.
Adjusti ng st
ud
R.
Ret urn fitti
ng
C.
Check
plug
T
.
Sig
ht tu
be
H.
High
spee d
needle
2.
Fu
el
pum
p diaphr agm
I. Idle needl e
4. Lower
gas
ket
surface
L.
Locknut
7.
Operating diaphragm
120
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