Cessna 172N - Page 125

CESSNA
MODEL
172N
SECTION
7
AIRPLANE
&
SYSTEMS
DESCRIPTIONS
lryise,
OFF,
R,
L, BOTH, and
START.
The
engine
should
be operated
on
both
magnetos
(BOTH
position)
except for
magneto
checks.
The
R and L
positions
are for
checking
purposes
and
emergency use
only.
When
the
switch
is
rotated
to
the spring-Ioaded
START
position,
(with
the master
switch in
the
ON
position),
the
starter
contactor
is energized
and
the
start-
er
will crank the engine. When the
switch
is released,
it wiII
automatical-
Iy return to the
BOTH
position.
AIR, IN
DUCTION SYSIE'}I
The engine
air
induction
system
receives ram air through an intake
in the lower
front
portion
of the engine
cowling. The
intake
is covered
by an air
filter which removes dust and other foreign
matter from
the
induction air. Airflow
passing
through
the filter
enters
an air
box.
After
passing
through the airbox,
induction
air enters
the
inlet
in the
carburetor which
is under
the engine,
and is then
ducted
to the engine
cylinders through intake
manifold tubes. In the event
carburetor ice is
encountered or the intake
filter
becomes
blocked, alternate
heated air
can
be obtained
from a shroud around
an exhaust
riser through a
duct
to a valve, in the
airbox,
operated by
the carburetor
heat control
on
the
instrument
panel.
Heated
air
from the shroud is
obtained
from
an
unfiltered
outside source.
Use
of
full
carburetor
heat at full throttle
will
result
in
a
loss
of
approximately
100 to
225 RPM.
EXHAUST SYSTEftl
Exhaust
gas
from each
cylinder
passes
through riser
assemblies
to a
muffler
and tailpipe. The
muffler
is
constmcted with
a
shroud
around the
outside
which
forms a heating
chamber
for cabin heater
air.
CAR.BURETOR
AND PRI'VIING
SYSTEftl
The engine is
equipped
with
an
up-draft, float-type,
fixed
jet
carbr.r-
retor
mounted
on the
bottom
of the
engine.
The
carbtrretor is equipped
with
an
enclosed
accelerator
pump,
simplified fuel
passages
to
prevent
vapor locking,
an
idle cut-off
mechanism, and a
manual
mixture
control.
Fuel
is delivered to the
carburetor
by
gravity
flow
from
the
fuel
system.
In
the
carburetor, fuel is
atomized,
proportionally
mixed with intake air,
and
delivered to the
cylinders
through intake manifold tubes.
The
propor-
tion
of atomized fuel to
air
is controlled,
within
limits,
by the mixture
control
on
the
instrument
panel.
For easy
starting
in
eold weather,
the engine
is equipped
with
a
manu-
al
primer.
The
primer
is
actually a
small
pump
which
draws
fuel from
the fuel strainer
when the
plunger
is
pulled
out, and injects
it
into the
cylin-
der intal<e
ports
when the
plunger
is
pushed
back
in.
The
plunger
knob, on
?
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