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lnlet
Needle
Floof
FIGURE
49
-
Fuel lnlet
System
floot,
opening
or
closing
the fuel
inlet
volve
to
immediotely
restore
the
prop-
er
fuel
level. The
fuel
inlet
system
must
constqntly mointoin this specifled
level
of
fuel
becouse
the
bosic
fuel
me-
tering
systems
ore
colibroted
to
de-
Iiver
the
proper
mixtures
only
when
the
f
uel is
ot
this
level.
ldle
Fuel
System
Fuel
for
idle
ond low
speed
opero-
tion
posses
through
the moin
metering
iei
into
the
moin
well ond from
the
moin
well into idle
possoges
where oir
is
introduced through
the idle
oir
bleed.
The mixture
of oir
ond fuel
is
dis-
chorged through
the idle
port
ond,/or
the tronsfer
slot.
The idle
fuel
mixture
is
controlled
by the idle
odiusting
needle
which
seots
in the idle
dischorge
hole.
Turning
the
idle odiusting
needle
in,
moves
its pointeci
tip
closer
to
the
seot,
restricting
the fuel flow
out
the idle
dis-
chorge hole. This
results
in
o
leoner
idle
mixture.
Conversely,
turning
the
needle
out,
moves
the
tip forther
from
the
seot, ollowing more
fuel
to
flow
out the
idle
dischorge
hole
for
o
richer
idle
mixture.
During
off-idle
operotion,
the
throt-
tle plote
is moved
slightly
post
the
idle
tronsfer slot, which begins
dischorging
fuel os
it
is
exposed
to
monifold
voc-
uum.
As
the throttle plote is
opened
still wider, ond
engine speed
increoses,
the
oir
flow
through
the
corburetor
is
olso
increosed. This
creotes
o
vocuum
in
the venturi
strong enough
to
bring
FUEL
_
CARBURETION
-
EXHAUST
Fuel
lnlel
Fitting
ldle
Aspirotor
Air
Bleed
ldle
Mixture Adjusting
Screw
ldle
Dischorge
Port
FIGURE
50
-
ldle
Fuel
System
t9
Mqin Well
Mqin Jet
Tronsfer
Slot
bil;zing
the fuel
dischorge
ond
moin-
toining
the
required mixture
rotios.
This emulsion
of
fuel ond oir,
being
lighter
thon
the
row fuel,
responds
foster
to
ony
chonge
in
venturi
voc-
uum.
lt
olso voporizes more
reodily
thon row fuel when
it
is
dischorged.
The
fuel
continues
up the
moin
well
ond
flows
out the moin
nozzle.
The throttle plote
controls
the
omount
of
the
fuel oii'
mixture
odmit-
ted to the intoke
monifold,
reguloting
the
speed onC
power output
of
the
en-
gine
in
occordonce
with
occelerotor
pedol
movement.
The distribution
pin,
on the moin
nozzle, diverts the
oir
flow
in the corburetor
to oid in
providing
proper distribution
of
the
mixture
to
oll
cylinders
of
the
engine.
The
moin
well
oir
bleed
prevents
si-
phoning
or fuel
percolotion
when
the
engine
is
shut
down.
Power Fuel
System
When
high-pov/er oiJtput is required,
the
corburetor
delivers
o
richer
mix-
ture thon thot
supplied
for
normol
cruising when no
greot lood is
ploced
on
the
engine. The
odded fuel
for
high
power operotion
is
provided
by
the
power
fuel
system, somelimes
colled
the
economizer
system.
At
higher monifold
vocuums,
the
vocuum piston is pushed
upword
in
the
possoge
ond
the
piston spring
is
com-
pressed (Fig.
52).
When engine
speed
or lood
reduces
the
monifold vocuum
to o
speciled
point,
the
piston stem
spring
exPonds
I
the
moin
fuel
metering system
into
op-
erotion. The
flow from the idle
system
topers
off
os
the
moin
fuel
metering
system
begins dischorging
fuel.
The
two
systems
ore
engineered
to
pro-
vide
o
smooth
tronsition
from idle
to
cruising
speeds.
Moin
Fuel
System
The
moin
fuel
system
consists
of
the
moin
iet,
moin
well,
moin
well
oir
bleeds
ond
o
moin
d:schorge
nozzle.
Air
drown
in by the
downword
movement
of
the
pistons
in
the
engine
posses
through
the
corburetor
venturi.
This
creotes
o
drop
o{ oir
pressure,
commonly
colled
vocuum,
in the
ven-
turi.
The strength
of
the
vocuun^
's pro-
portionol
to
the
omount
of oir
being
cirown
through
the
venturi, which,
in
turn, is
governed
by the
speed
ond
power outpui
of
the
engine.
At
normol cruising
speeds,
the
dif-
ference
in
pressure
between
the
nor-
mol
oir
pressure
in the
top of
the floot
chomber
ond the
vocuum
in the
ven-
turi,
forces
o
metered
flow of
fuel
from
the floot
chomber
through
the
moin
metering
system
ond out the
moin
noz-
zle, which
is
locoted
in
the
venturi.
The
fuel is
metered
(or
meosured) by
the
moin
jet
os
it
flows
into
the
bot-
tom
of
the
moin
well
(Fig.
5l).
Filtered
oir
from
the
corburetor oir
inlet
posses
through
the
high
speed
bleed
ond
enters
the fuel flow in
the
moin
well.
The
high
speed
bleed
me-
ters
o
properly
increosing omount
of
oir to the fuel
ot
higher
speeds,
sto-
tl
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