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Carburetor Service
ENGINE~
Fig
.
14-Exploded view of
operating
diaphragm
(7),
spr
ing
(8),
spring
seat (9)
and regulator cover (10).
Upper end of adjusting
stud is shown at (A).
5---,. . . . . . .
;--11
16
17
Fig. 12-Exploded
view
of KEIHIN d
iaphragm
type carburetor showing component parts.
Sight
tube (21) is used to set fuel level and
.
is not a part of the
carburetor.
I.
Throttle
body
2.
Low speed
screw
12.
Bleed plug
3.
High speed needle
13.
Spring
4.
Low
speed
need
le
14.
Pivot
shalt
5.
Pump
diap
hragm
15.
Valve
lever
6.
Pump
upper
cover
16.
Regulatin g
diaphrag m
7.
Gasket
17.
Spri
ng
B.
Pump
check
valves
l
B.
Regulator cover
9. Pu
mp
(regu
lating)
body
19.
Lock screw
10.
Inlet
fitti
ng
20.
Adjust ing scre w
11. Inlet
needle
&
seat
21. Sight tu
be
Fig.13-0perating diaphragm (7) and associ
ated parts installed on lower side of valve
body.
7. Oper ating diaphr agm
B.
Spring
P
.
Pulse
fitti ng
9.
Spring sea
t
R.
Return
fittin
g
F. Inlet
fuel
fitting
X.
Fuel
passages
good pin punch of
appropriate
size,
drive
valve
sea
t
(V)
1I ,V••
>I
out of
valve body.
Valve h,ts
are
available
in sta
ndard
size
and OD
oversi zes
of
0.01
, .d
0.002
mm.
Oversize valves
a
"il
t'
iied by one or two annular
<J"'S
around
outside
of body while
s
ta
ndar d body
is s
moot h.
Rein stall
retainer
(R-Fig.
10), needle valve
and
lever, then check height
of
actuating
button
(B-Fig.
11)
which
should
be
flush
with
valve body floor.
Adjust
if
ne
cessary
by
bending
t
ang
w
hicl
contacts
valve needle
(N).
Fig.
13 shows
operatin g
diaphr
agn
(7), spring
(8)
and spr
ing seat
(9
corr
ectly positioned. Parts
are
show
r
exploded in proper
order
in
Fig.
14.
Ar
initial starting point for adjus
t ing
st ue
(A) in
regulator cover (1
0)
is
with
tWI
thr
eads showing when viewed
fron
inside as
shown.
Adjust
the
assem
bled
carburetor
after installation
as
previ
ously
outlined.
KEIHIN
TYPE FLOAT CARBURETOR
WITH BUTTERFLY THROTTLE
Carburetors
are identified by
a
model
number which
consists
of a let
ter
prefix
"BD"
followed
by a set of
numbers
such
as
"44-38".
Fir
st part
of
number in
dicates
throttle bore
(in millimeters) and
second
part
of number
indicates
venturi
diameter.
ADJUSTMENT
FLOAT LEVEL.
Float
is
adjusted by
bending
metal tang
between float body
(16- Fig
.
14A) and
float
pin
(17).
As
shown in Fig. 14B,
distanc e
(D) should
be 0.48-0.67
inch
when
carburetor
is
tilted
~t
a 20-30 degree
angle.
IDLE SPEED.
Idle
speed is
adjusted
by
turning
screw (8-Fig.
14A).
Idle
speeds vary
from model to model, con
sult resp
ective
manufacturer specifica
tion
for
recommended
speed
setting.
IDLE MIXTURE.
Idle mixture
ae
justment is
done by turning
sere.
(6- Fig
.
14A).
Start engine and bring
u
to normal
operating
temperature. Tur
screw
eith
er
in
(lean)
or out (rich)
to
ot
tain an even engine
idle.
Readju
st
idl
speed to recommended
setting after
idl
mixture
is
set.
MAIN JET.
To insur e
top
perforn
ance of engine, main
jet (13-Fig.
14. . 1
may need to
be
changed
if
there
is
:
2000 feet change in
altitude
or an
1:
degree
F
change
in
temperature.
Whe:
altitude or weather temperature
if
creases a lower
number of jet
should
b
used. Whenever altitude or
weathe
temperature
decreases
a larger
numbe
of jet should be
used.
Caution
should
b.
taken especially when
operating at
.
lower altitude, too
lean of fuel
mixtur.
could shorten engine
life.
.
•
..
~
~'I~
'
"
. . . . . . '
h.
: ,l......,,{.
"'~.
• ..
tj;..~..
.."
\
~
.
122
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