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3.7 CARBURETOR
-=·
-.=:--=..
=
-~
:·
·:eo e
in
conjuncrio·
-·
e ·eeo e
jet
::::
-
=~=
e::-
·er,
regula
tes
e
.e
--
-
~"e
at
the
-,--:-::.
::-e
-
rottle ope
ning p(·::·
b
eiween ~
-
_
---~
-
e
o
peni
ng!.
The
long
·ooered jet
needle
-
·::::-eo
centr
ally
w
ithin
he
cen·
er hol
e o
f
the
--·::- e
:alve
and w
ith the
oper
ed
end
i nserted
into
··e
·eedle
jet.
The
vertica
l
moveme nt o
f
the throttle
a
.e
o
w
hich the
jet
needle
is
attached contro
ls
the
"o" o
f
the fue
l
in
respect to
the
throttle
opening
to
afford
a co rrect fuel mixture ratio.
There
are five
ne
edle
clip grooves
!which
are counted from
the to pl
to
reg ulate
the richness
of
the fuel
mixture.
The
fuel
mixture becomes
richer as
the
clip
is moved
progres-
sively from
the
No.
1
groove to
the
No.
5
groove.
(Fig.
3-
99)
e.
Throttle
valve
The
function of
the throttle
valve
is
to
co ntr
o
l
the amount of
air token into the
engine
which
serv
es
to
increase the
engine
RPM
and the
pow
er
output,
a
nd in
addition, performs the important
function
of
controlling the
fuel
air
mixture
.
(Fig.
3-1
00)
The
thro
ttle
valve
is
cut-aw
ay
on
the
air
inlet
side. By changing the
size of the
cut-aw ay
(designate
d
by cut-away
No.l
t
he
pressure actuating
t
he ne
edle
va
lve
ca
n
be altered
to change the
amo
unt
of
fu
el
now and causes a change to
the
fue
l
mixture.
The
valve
with a
larger
cut-away number
w
ill
produce a
leaner
fuel
mixtu
re.
However, the
range of
its effec-
tiveness
is mai
nly
at
low
speed from
idling
speed to
approximately
~ thro
ttle openi ng.
It has
no effect
beyond
;%
throttle
opening.
The
throttle valve
is
normally
opera
ted by the
throttle
cable
attached to
the top
of
the
carburetor.
A
throttle stop screw keeps
the
throttle
va
lve
in
the
idle position.
Turni
ng
the stop screw
in
will
cause
the
throttle
valve to rise, and backing
off o
n the
stop
screw
w
il
l
lower
the
thro
ttl
e
valve
.
(Caution)
The
throttle
valve guide groove
serves
as
a
junction for
the
throttle
cable
and
the
throttle
valve and also
to
maintain
the throttle
valve
in the
correct relative position within
the
carburetor,
therefore
,
if it
is
reve rsed, the
cut-away
w ill
be on
the wrong
sid
e
and will
resu
lt
in rich
fu el
mixture
as well
as
causing insuffici
ent engine
speed.
f
.
Slow jet
The slow
jet
regulates
the
fuel
now during idling
and small throttle opening,
a
nd p ermits th
e
air t
o
ent
er
th
rough the
air
bleed
to
mix
with
the
fuel
for
atomizatio
n.
The slow jet is similar
to
th
e
main
jet i
n
that th
e
larger
the jet
size
number, the greater will
be the
fue
l
now
and
consequently
a richer fuel air
mixtur e.
(Fig.
3-101)
Figure 3-99.
Jet needle
Figure
3-100.
Throttl
e valve
Fi
gure
3-101.
Slow
jet
41
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