Cessna T188C - Page 197

MODEL
188 & T188
SERIES SERVICE
MANUAL
11A-34. FUEL-AIR CONTROL UNIT. This unit oc- air throttle lever. The idle mixture adjustment is
cupies the position ordinarily
used for a carburetor,
the locknut at the metering
valve end of the linkage.
at the intake manifold inlet. The function of this unit Tightening the nut to shorten the Linkage provides a
is to control engine air
intake and to set the metered
richer mixture. A leaner
mixture is obtained by
fuel pressure for proper fuel-air
ratio. There are
backing off the nut to lengthen
the linkage. Adjust
three
control elements in this unit,
one for air and mixture
control to obtain a slight and
momentary
two for fuel.
One of the fuel control elements
is for gain of 50 rpm
maximum at 1000 rpm engine
speed
fuel mixture
and the other
is for fuel metering.
Fuel
as mixture control
is moved
slowly from full
RICH
enters the
control unit
through a strainer
and passes
toward idle
cut-off. If
mixture is set
too LEAN,
to the metering
valve. The
position of the
metering
engine speed
will drop immediately,
thus requiring
valve
controls
this fuel passed
to the
manifold
valve
enrichment.
If
mixture is
set too RICH,
engine
and
nozzles. A linkage connecting
the metering speed
will increase above 50 rpm,
thus requiring
valve to
the air throttle
proportions airflow
to fuel
leaning.
Idle speed is
approximately
600 rpm.
flow.
The position
of the
mixture valve
determines
Refer to figure
11A-4.
the amount of fuel returned to the fuel pump. The
fuel control
portion of
the fuel-air control
unit is
11A-38.
RIGGING THROTTLE
- OPERATED
enclosed
in a shroud
and is blast-air
cooled
to help
MICROSWITCH.
Refer to
Section 16.
prevent
vapor
lock.
11A-39. ELECTRIC
FUEL
PUMP CIRCUIT.
Refer
11A-35. REMOVAL
AND INSTALLATION.
to Section 12.
a. Place
all cockpit
switches and
fuel shut-off valve
in the OFF position.
11A-40. AUXILIARY
ELECTRIC FUEL PUMP
b. Remove lower
cowl section
in accordance
with FLOW
RATE ADJUSTMENT.
Refer to Section
12.
paragraph
11A-3.
c.
Remove induction
airbox
in accordance
with
11A-41.
FUEL MANIFOLD
VALVE (FUEL
DISTRIB-
paragraph
11A-55.
UTOR).
Metered
fuel flows
to the fuel
manifold
valve,
which provides
a central
point for distrib-
NOTE
uting fuel to
the individual
cylinders.
An internal
diaphragm,
operated
by fuel pressure,
raises or
Cap
all disconnected
hoses, lines
and fittings.
lowers
a plunger to open
and close the
individual
cylinder
supply
ports
simultaneously.
A needle
d.
The three
fuel lines
which attach
to the
fuel con-
valve
in the plunger
ensures
that the
plunger
fully
trol
unit are
routed inside
flexible
tubing
to help cool
opens
the outlet
ports
before fuel
flow starts
and
the
fuel.
Loosen
the tubing
clamps
at the
control
unit
closes
the ports
simultaneously
for
positive
engine
and slide
the tubing
back to
gain access
to the
fuel
shut-down.
A fine-mesh
screen
is included
in
the
line
fittings.
fuel manifold
valve.
e. Disconnect the fuel lines at the control unit.
f. Loosen
the hose
clamps
which secure
the control
11A-42.
REMOVAL.
unit
to the
right
and
left
intake
manifolds.
g. Remove
the control
unit.
NOTE
h.
Cover the open
ends of the
intake manifold
pip-
ing to
prevent the entry
of foreign matter.
Cap
all disconnected
lines, hoses
and fittings.
i.
Reverse the
preceding steps
for reinstallation.
Use
new gaskets
when installing
control
unit.
Rig
a. Disconnect
the fuel lines
and the
six fuel injec-
throttle
and mixture
controls in
accordance
with para-
tion lines
at the fuel
manifold.
graph
11A-63
and 11A-64
respectively.
Rig
throttle-
b.
Remove the
two crankcase
bolts
which secure
operated
microswitch
in accordance
with
Section 12.
the
fuel manifold
and
remove the
fuel manifold.
11A-36. CLEANING AND INSPECTION. 11A-43. CLEANING.
a. Check control connection,
levers and linkage for
a. Remove fuel manifold
valve from engine and re-
security,
safetying
and for lost
motion due to
wear. move
safety wire
from cover attaching
screws.
b. Remove
the fuel screen
assembly and
clean in
b. Hold the
top cover down
against internal
spring
cleaning solvent.
Reinstall
and safety.
until all four
cover attaching
screws have been
re-
c. Check the air control body
for cracks and control
moved, then gently lift off the
cover. Use care not
unit
for overall condition.
to damage
the spring-loaded
diaphragm
below cover.
c.
Remove
the upper
spring
and
lift the
diaphragm
11A-37.
ADJUSTMENTS.
The idle
speed adjustment
assembly
straight up.
is a
conventional spring-loaded
screw
located in
the
11A-13