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Servicing Carburetors
Section
3
WYM
Carburetors
WYM Barrel
Valve Carburetor
Saw
Models 300
and
300S (Fig
ure
3,30)
Fuel Flow
(Figure 3,29)
Walbro
WYM
carbure
ors fe ature a
single
fu
el nozzle
inside
an
ad
ju stabl
e
venlur
í
or
barre/
va/ve,
Ro
tati
ng the
barrel
valve
cause
s
more or le
ss
of
lhe
ven
tUf
I
to
be
exposed,
co ntrolling
airflow
ith
in
the
carburetor, The
fuel
nozzle
is
loca
ted
al
the
cenler
01
the
airstream in
the
venturi,
allowing nearly
instant
th rottie
response
at
any
throt
tle
settin
g
,
• Fu el
fl
ow
at
idle
ca
n be
adju
sted
by rais
ing
or
loweri
ng an
"Iow
idle
needle"
(d
olted
line
in
illu
stra
tion)
in
the
WYM
nozzle
,
•
Fuel
fl
ow at
or
near
full
throttle
setti
ng IS
deter ined
by
the
size
of
a
replaceable
let
orilice
located
within
the
car
bu
retor
body,
and is no
t
otherwi
se
adjustable,
Dissassembly
(Figure
3,3
1)
STEP 1.
Unscrew
the
fou
r
metenng
cover
reta ming
screws,
and
hen
remo ve
th
e
meteri
ng
cover
STEP 2.
Gen
tl
y
peel
th
e
metering
diaphragm
Irom
he
pump
body ass
em
bly,
and lhen
lift
the
pum
p body
[ram
th
e
carbureto
r body,
STEP 3.
Using a
sma
ll
scre dr iver,
gently
pry
lhe
metering lever
assembly from
the
pump
body,
IMPORTANT!
The
WYM inlet
needle valve
can be
removed
la
r
cleanin
g
,
bu
t
is not
available
as
a
separate
par!
nurnber
!
WVM at
Id le
Idle
Needle
Throttle ---_~~~==¡T'
Lever
Lowered
and
Ramp
Air Flow
Fuel
lo NozzleO
WVM at Wide
open Throttle
Idle
Needle
Raised
Air
Flow
Figure
3.29
WYM
Carbure/or
(Models
300
and
3005)
Idle~
~
Idle
Speed
.
'"
AdJusllng
~
'¡¡:
Brackel
Screw
~
/
§
I
j//
i.
L -
LOW
Idle
I
Needle
Barrel
Valve
Carburelor
Body
(J
Y!'~
MainJel _ _
&
~
and O-ring
~
Choke
Plale
~
Fuel Pump
~
Gaskel,
Plale and
Di
aptlragm
~
~
Inlel
Screen
~
~
~
PumpBody
"
B
e
?'"
,~
~
Metering
•
Q;
r-
Gasket
,
Diaphragm
and
Cover
O
1.
·
CRe-55
FIgure
3,30
The
WYM
Carbureror
Figure
3,3
WYM Carbure/or (Iypical)
'
~
Shindaiwa
Inc
1995
35
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