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Fig
.
2·58.
1.
Ad jus ling
screw
2.
Rubber
ri
ng
3. (over
4.
N ul
5.
Spri ng
6.
Dr
illi
ng lo unders ide
of diap hragm
VOLVO
103
636
By-pass va lve
7.
Diaphragm
8.
Ou
ll
el channe
l
fo
r
fue l/air mix ing
9.
Va lve
10.
Inl el
channe
l
for
fue l/a ir
mixin
g
11
.
Prim
ary
Ih rofll
e
turns and closes t he inlet
·
t o t he cha nnel. At t he sa me
tim
e as t he
cam d isc is opera.ted
,
the
th rottl
e f lap
o
pening
is a
lso
inf
lu en
ced
in such away
t
hat
t
urning
the cam di
sc
opens the throttl
e
th'rough the
f
ast id
le
stop screw (4, Fig.
2-52)
and the lever, before any of
the cal,ibra.ted holes open .the connection to the fuel
drilling. With
this arra
ngement, the idling speed can
if necessary
be ra
ised by the driver of the vehide
during the
wa1
r
ming -up period
of t he
engine.
IDLlNG
Wnen the engine is idling, the v O'cuum in the car-
burettor suction
char
mber is low and
,
t he column
bet-
ween the vacuurm plu.ng er and .the hridge will be small
(see Fig.
2-56)
.
At thi
s
stage, cthe
t
hi cker section of the
metering ne edle is i,n the jet and thus onlyasmall
quantity of fuel,co
l 1
responding to idling 'requirements,
is sucked into the engine. The tempelrature compen-
sator (Fig.
2-55)
is regula-ted bya bi -metal spring (4)
which in f.luences a valve
(3).
Wh en the engine is warm
and the temp eratu're in the carburettor ·rises, the valve
opens and ·air is obtained in the ,carburettor venturi
,
t o
'
c ompensate for cthe increase in the fuel flow, which
is obtained due to the aheration in the fue./'s visoosity,
see Fig.
2-56.
-F
ine a,djustment of the engine idling
speeld can be carried out with the id le trimming screw
(2,
Fig.
2-55).
NORMAL RUNNING
Wi,
t h the open ing of the throttle flap, engine indvc-
tion manifol,d depression is transferred via the chan
-
ne
l,
s
in
the p
lunger to the
sudion chamber which is
sea led
from the ma
in
body of the
carburettor
by the
d iaphragm.
The
press u·re d ifference between the un-
ders
id
e
of th
e air
va lve,
w here t
here
is pre ssure
in
th
e
carburettor inlet
port,
and the upper sid
e
of th
e
va-Ive,
w here t here is vac uum, ca uses the va,lve to
lif!- from the br
idge.
Th is a lso lifts t he tapered
me-
tering need le
(15,
Fig.
2-55),
w
hi ch
is attac hed to t he
p
lun
ger, out of t he
jet.
The effective choke a,rea and
t
hu
s a lso t he f
uel
f low
increase.
See Fig.
2-57.
As t he
v
ac
uu
m
in
t he eng
in
e ind uction man ifo ld is
dependent upo
n
t he eng ine speed and load, the
COf-
rect ·f
uel
f low is obta ined under
0'11
operat
in
g cond i-
tions
.
Beca,use of the var iab le choke area between the
bridge and
thc
va-
Ive, the ai,r ve,locity and pressure
drop a cross t he jet orifice w ill a lways rema in approx-
imate ly constant, thus ensur ing good f
ue·1
atom ization
at a
ll
spee,ds.
ACCELERATION
To
prov
ide at
an
y
po
int
In
the
t
h
ro t~
l
e
ra nge a tem
-
porary riche r mi
x,
t
ure aJ t he m
om ent
t he t hrott.le is
sudd en ly
o
pened
, a
hydrau1
lic ,damp er i
s a rra
nged
inside the va'lve rod.
The
hydrau,lic
d am
pe
r co
nsist
s
of a plunger
mo
unted on a
,
r
od
.
The plung er
ope,rates
in oil. When the throttle
is
sudd enly open ed,
t he
vacuum in the suction chamber
,increases
rapidly.
When
,
t he
air valve
(10,
Fig
.
2-55)
<lifts,
t he da
mper
piston (7)
is f orced a gainst
its seat and oil
is pre-
ventedfr.om flowing past from th
e
upper side the
lower side of
t
he damper plunger, this retarding the
movement of the valve
(10).
This tempora
r
ily
results
in a more
powerfu-
I vacuum above the jet so that the
fuel -air mixture becomes for the moment
richer.
The downward stroke of the air valve is assisted by
the spring
(6).
The ,rod in the valve should be filled
to approximately within a
1/4"
from
t
he upper ed ge
with oil which is approved
as
"Automatic Transmission
Fluid,
Type
A"
.
EXHAUST EMISSION CONTROl SYSTEM
The engine
'
is equipped with an exhaust emission
controi system in accordance with the ,principle of a
more complete combustion which reduces the contents
of ca'rbon monoxide and hydrocarbons in the exhaust
gases ,to an acceptable level. This is achieved mainly
by a modified
indu~ion
system that enables a more
exact and leaner mixture ratio between fuel and air
to be used.
How the system works is iHustrated in Fig.
2-59.
The intake manifold is fit.ted with a secondary throttle
2
: 27
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