1953 JEEP CJ seat adjustment

Dl

DAUNTLESS
V-6
ENGINE
DM.
GENERAL

This
section describes service and repair of the
Dauntless V-6 engine. The
engine
code
number shown in
Fig.
A-4 is provided to identify the Daunt­

less
V6-225 engine. The meaning of the coded letters and numbers that are stamped on the right front face of the crankcase, just below the rocker
arm
cover,
between
exhaust manifold ports, is given
below.
Letter
to
Designate
Market

M
—
Military
E
—
Export

D
— Domestic
Letter
to
Designate
Year
Built

N
— 1967
P
— 1968

R
— 1969
S
— 1970

T
— 1971

Letter
to Designate
Engine
and Compression
Ratio

H—V6-225
9.0 to 1
C.R.
(2 Bbl.
Carb.)
Y—V6-225
9.0 to 1
C.R.
Marine
(Low
Profile)
(2
Bbl.Carb.)
Z—V6-225
9.0 to 1
C.R.
Marine
(High
Profile)
(2 Bbl.
Carb.)

K—V6-225
7.6 to 1
C.R.
(2 Bbl.
Carb.)
L—V6-225
7.4 to 1
C.R.
(2 Bbl.
Carb.)

Market

Domestic
—

Year
"1967"
Engine
J

Day

Plus Chg. If
Any-
Service Engine "S"
Short
Block
"R" -Oversize Bores "B"
Undersize Crank

&
"A"

Rod
Bearings

The
identifying letter or letters follow the
engine
letters are decoded as follows:
A—.010"
Undersize
Main
and Connecting Rod
Bearings

B—.010"
Oversize Pistons

AB—Combination
of A and B
S—Service
Engine

R—Short
Block

All
disassembly and assembly procedures are pre­ sented in logical order, assuming a complete
engine

overhaul
with
engine
removed from the vehicle.

However,
many of
these
procedures can also be
performed as on-vehicle services if vehicle or
engine
components are removed to gain access to parts
involved.

Note:
Some
engines
are equipped with an exhaust
emission control system. Service information on
the components of this system is given in sec­ tion F2.

Dl-2.
ENGINE
DESCRIPTION

The
Dauntless V-6
engine
has a displacement of
225 cubic inches. It has a compression ratio of
9.0 to 1, which permits use of regular-grade
gaso­

line.
See
Figs.
Dl-1 and Dl-2.

The
cylinder block is made of cast
iron.
Two banks
of cylinders (three cylinders per bank) are cast at a
90-degree
angle. The lower part of the cylinder-

block
extends
below the centerline of the
crank­
shaft, forming a continuous flat surface with the

rear
crankshaft main bearing cap and the timing

chain
cover.
This
design allows installation of an
oil
pan with a
one-piece
gasket. The cylinders in
the left bank (as viewed from the driver's seat) are
numbered
1-3-5,
from front to
rear.
The cylinders

in
the right bank are numbered
2-4-6,
from front
to
rear.

The
crankshaft is supported in the cylinder block
by four steel-backed full-precision bearings, all of

which
have an identical diameter.
Crankshaft
main bearings are numbered 1 to 4, front to
rear.
The

thrust
bearing is flanged to maintain crankshaft position and to compensate against crankshaft end

thrust
The No. 2 bearing is the thrust bearing.

The
crankshaft is counterbalanced by weights,
which
are cast integral with the
crank
cheeks. The

weights
are shaped to a contour which
gives
mini­
mum
clearance with cylinder barrels and piston

skirts
to conserve space.

Connecting
rods have I-beam sections with
bosses

on each side. Metal is removed, as required, to secure correct weight and balance. The lower end
of each connecting rod has a steel-backed preci­
sion bearing. The piston pin is a press fit into the upper end. The outer ends of the piston pin

are
a slide fit in the piston
bosses.

The
full-skirted, aluminum alloy pistons are cam ground and tin plated. Two compression rings and
one oil control ring are installed above the piston
pin.
The cast iron compression rings in the two

upper
grooves
of the piston have a
groove
or bevel cut around the inner
edge
on one side. The
top compression ring is installed with this
groove
or
bevel up. The lower compression ring is installed

with
bevel down. The oil
ring,
in the lower groove,
consists of two thin steel
rails
separated by a

spacer.
It is backed by a hump-type spring-steel
expander.

V-6
engine
cylinder heads are made of cast
iron.

Their
valve
guides
are cast integrally. Right and left cylinder heads are identical and interchange­
able. In service, however, it is
good
practice to
install
the cylinder heads on the side from which
they were removed.

The
valves are in line in each head, at an angle
10°
above the centerline of the cylinder bores.

Each
valve has a spring strong enough to ensure
positive valve seating throughout the operating speed range of the engine. The valve rocker arm
mechanism is protected by a
sheet
metal cover.
This
cover is seated on a raised surface of the
cylinder
head. It is gasketed to prevent oil leaks.

The
rocker arms for each bank of cylinders are mounted on a tubular steel shaft, supported on
the cylinder head by brackets. The rocker arms
are
made of aluminum. They have inserts at the

push
rod socket and the valve stem contact face.

The
camshaft is located above the crankshaft be­
tween the two cylinder banks; it is supported in
four steel-backed babbitt-metal bearings. The cam­ shaft is driven at one-half crankshaft speed by
sprockets and a single outside-guide type chain.

Hydraulic
valve lifters and
one-piece
push rods operate overhead rocker arms and valves of both

banks
of cylinders from a single camshaft.
This

system requires no lash adjustment during assem­
bly
or in service.

In
addition to its normal function of a cam follower,
each hydraulic valve lifter also serves as an auto- 76

Dl

DAUNTLESS
V-6
ENGINE
Dl-38.
Crankshaft
Cleaning

Clean
the crankshaft thoroughly with a suitable
cleaning solvent.
Clean
drilled oil
passages
in its

journals
with a small rifle brush to remove all
sludge
or gum deposits; dry
passages
with com­
pressed air.

Dl-39.
Crankshaft
Inspection
and
Repair

If
the crankshaft has not
been
removed from the

cylinder
block for inspection, disconnect two con­ necting rods at a time from crankshaft. Inspect
the bearings and crankpin journals. While turning
crankshaft,
it is necessary to temporarily reconnect
the rods to crankshaft to avoid possibility of dam­ aging the journals through contact with uncon­
nected rods.
Inspect the crankpins visually for excessive or ir­

regular
wear, and for scoring. Use an
outside
micrometer to check crankpins for out-of-round.
Standard
crankpin
diameter is
2.0000"
[5,080
cm.].

If
crankpins are more than .0015"
[0,0381
mm.]
out-of-round, new bearings cannot be
expected
to
have satisfactory life.
If
the crankshaft has
been
removed from the
cyl­

inder
block for inspection support it on V-blocks
at its main bearing journals 1 and 4. Inspect the

main
bearing journals visually for excessive or ir­

regular
wear, and for scoring. Standard main bear­
ing
journal
diameter is 2.4995"
[6,349
cm.].
Total

indicator readings at each
journal
should not ex­
ceed .003"
[0,076
mm.].

Check
run out at all four journals and
note
high
spot
(maximum eccentricity) of each
journal.
High

spot
of each
journal
should
come
at the same
angular
location. If high
spots
do not coincide,

crankshaft
is misaligned and unsatisfactory for
service.

If
crankpin or main bearing journals are scored,
ridged, or out-of-round, the crankshaft must be replaced or reground to a standard undersize bear­
ing diameter to ensure satisfactory life of bearings. Slight roughness can be removed with a fine grit
polishing cloth thoroughly
wetted
with
engine
oil.
Burrs
can
be
honed with a fine oil
stone,
so long as
bearing clearances
will
remain within specified
limits.

Dl-40.
Crankshaft
Main
Bearings

A
crankshaft bearing consists of two halves which
are
neither alike nor interchangeable. One half is

carried
in the corresponding main bearing cap; the
other half is located
between
the crankshaft and

cylinder
block. The upper (cylinder block) half
of the bearing is grooved to supply oil to the con­ necting rod bearings, while the lower (bearing cap)

half
of the bearing is not grooved. The two bearing
halves must not be interchanged. All crankshaft
bearings
except
the thrust bearing and the
rear

main
bearing are identical. The thrust bearing (No. 2) is longer and it is flanged to take
crank­

shaft end thrust. When the bearing halves are
placed in cylinder block and bearing cap, the
ends
extend slightly beyond the parting surfaces. When
cap
bolts
are tightened, the halves are clamped
tightly in place to ensure positive seating and to
prevent turning. The
ends
of bearing halves must never be filed flush with parting surface of
crank­

case or bearing cap.

Crankshaft
bearings are the precision type which
do not require reaming to size or other fitting.
Shims
are not provided for adjustment since worn
bearings are readily replaced with new bearings of proper size. Bearings for service replacement are

furnished
in standard size and undersizes. Under no circumstances should crankshaft bearing caps
be filed to adjust for wear in old bearings.

Dl-41.
Crankshaft
Main
Bearing
Cleaning
and
Inspection

Clean
main bearing surfaces. Inspect the bearings

visually
for excessive or uneven wear, scoring, and

flaking.
Visibly worn or damaged bearings must
be replaced. It is necessary to check
radial
clear­ ance of each new or used crankshaft main bearing
before installation.
This
can be
done
by either of two methods, which are described in
Pars.
Dl-42

and
Dl-43.

a.
The desired
radial
clearance of a new bearing
is .0005" to .0021"
[0,0127
a
0,0534
mm.].
b. Replacement bearings are furnished in standard
size, and in several undersizes, including undersizes
for reground journals. If a new bearing is to be installed, try a standard size; then try each under­
size in turn until one is found that
meets
the
specified clearance limits.

Note:
Each
undersize bearing half has a number
stamped on its outer surface to indicate amount of undersize. Refer to Fig. Dl-12. 14288

FIG.
Dl-12—LOCATION
OF
UNDERSIZE
MARK
ON
BEARING
SHELL

1—
Tang

2—
Undersize
Mark
Dl-42.
Main
Bearing
Fitting,
Plastigage

Bearing
clearance can be checked by use of Plasti­
gage,
Type PG-1 (green) which has a range of
.001" to .003" [0,025 a
0,076
mm.]. Refer to

Fig.
Dl-13.

a.
Place a piece of Plastigage lengthwise along the
bottom
center of the lower bearing half, then 86

FUEL
SYSTEM

14261

FIG.
E-6—CARBURETOR—
F4 ENGINE,
LATE
MODEL 1—
Choke
Clamp Bracket
2—
Throttle
Lever
and Shaft
3—
Choke
Shaft and
Lever

4—
Bowl
Vent Tube
5—
Fuel
Inlet Elbow
6—
Dash
Pot Bracket 7—
Throttle
Lever
8—
Dash
Pot Plunger
9—
Dash
Pot Assembly
10—
Lock
Nut
11— Stop Pin

1
2—Idle Mixture
Limiter
Cap
13—
Idle
Speed Adjusting Screw 14—
Fast
Idle Connecting Rod
E-11.
Float System

The
float system, Fig. E-7, consists of a float,
float
pin,
air horn gasket and the
needle
and seat assembly. These parts control the fuel level in the

carburetor
bowl, a supply being maintained for all
systems under all operating conditions. To prevent
float
vibration
from affecting the fuel level, the
inlet or float valve is spring loaded. Should the

needle
and seat
become
worn, they must be re­
placed
with a matched set, including the spring,

which
is the only way they are supplied. When
reinstalling
the float, be sure to install the float pin

with
the
stop
shoulder on the side away from the bore of the carburetor.

E-12.
Float Adjustment

Correct
float level setting is required for accurate
metering of fuel in both low- and high-speed jets.

To
set the float, remove and invert the bowl cover. Remove the bowl cover gasket. Allow the weight
of the float to rest on the
needle
and spring. Be

sure
there is no compression of the spring other

than
the weight of the float. Adjust the level by
bending the float arm lip that contacts the
needle
(not the arm) to provide specified clearance be­
tween the float and cover. The specified clearance of the float is
L74\F
[6,74 mm.] on current models
(including
Exhaust
Emission Control) and [7,93 mm.] on early models shown as A in
Fig.
E-8.
FIG.
E-7—FLOAT SYSTEM
1—
Float
and
Lever
Assembly
2—
Needle
Valve and Seat Assembly

3—
Vent

4—
Float
Bowl Cover 5—
Float
7 '.. j
io8Si
i

FIG.
E-8—FLOAT
LEVEL
GAUGING
E-13.
Low-Speed System

Fuel
for idle and early part-throttle operation is
metered through the low-speed system. The low-
speed system is illustrated in Fig.
E-9.
Liquid
fuel enters the idle well through the metering rod jet.

Low-speed
jet measures the amount of fuel for
idle and early part-throttle operation. Air-by-pass,
economizer, and idle air bleed are carefully
cali­

brated
orifices which serve to break up the liquid
fuel
and mix it with air as it
moves
through the passage to the idle port and idle adjustment screw

port.

E-14.
Idle Mixture Adjustment

Note:
The idle mixture adjustment procedure for
the late model
YF-4941S
and
YF-6115S
Carter
Carburetor
equipped with the
External
Idle

Mixture
Limiter
Cap is the same as outlined below 114

'Jeep*
UNIVERSAL
SERIES
SERVICE
MANUAL

E

FIG.
E-9—LOW-SPEED
SYSTEM

1—
Body
Flange 6—Idle Air Bleed

2—
-Idle
Adjustment Screw Port
7—Air
By-pass
3—
Idle
Port 8—Economizer

4—
Idle
Well
9—Metering Rod Jet
5—
Low
Speed Jet 10—Idle Adjustment Screw
in
Pars.
"A"
through
"D";
however, because of the

Idle
Limiter
Cap,
the idle mixture screw
CANNOT

be adjusted in the counter-clockwise
(rich)
direc­
tion. The adjustment is made from the
rich
stop

position and the mixture screw is turned in (clock­
wise) approximately %
turn
to
"Lean
Best
Idle."
Refer
to Fig. E-6.

The
"Lean
Best
Idle"
method of idle
setting
is as
follows:

a.
Any scheduled service of ignition system should precede this adjustment.

b.
Connect tachometer or vacuum
gauge
to
engine.

c.
Warm
up
engine
and stabilize temperatures.

d.
Adjust
engine
idle to
speed
desired, using throt­tle idle
speed
adjusting screw.
e. Carburetors without Idle
Limiter
Cap
turn
idle
mixture
screws out (counterclockwise) until a
loss

of
engine
speed
is indicated; then slowly
turn
mix­
ture
screw in (clockwise
-leaner)
until maximum

speed
(RPM) is reached. Continue turning in (clockwise) until
speed
begins
to drop;
turn
mixture
adjustment back out (counterclockwise
-rich)
until
maximum
speed
is just regained at a "lean as
possible" mixture adjustment.

E-15.
High-Speed System

Fuel
for part-throttle and full-throttle operation
is supplied through the high-speed system shown

in
Fig. E-10. A metering rod and metering rod

jet
control the amount of fuel admitted through the nozzle for high-speed operation. The lower
end of the metering rod is calibrated in size to

accurately
meter the fuel required. As the rod
|
13346

FIG.
E-10—HIGH-SPEED
SYSTEM

1—Nozzle 7—Pump Diaphragm
Spring

2
—Metering
Rod 8—Diaphragm Assembly

3—
Pump
Lifter
Link
9—Chamber

4—
Metering
Rod Arm Assembly
10—Metering
Rod Jet 5—
Diaphragm
Shaft
11—Carburetor
Casting

6—
Upper
Pump Spring 12—Carburetor Bore is automatically raised and lowered in the jet,
the opening in the jet is varied in size to supply
fuel
proportionate to the requirements through the
higher
speed
and power range. The metering rod
is both mechanically and vacuum controlled and is
attached to the metering rod arm assembly.
During
part-throttle operation, vacuum in chamber

pulls
diaphragm down, holding metering arm
assembly against pump lifter
link.
Movement of the metering rod is controlled by the
pump lifter
link
which is attached to the carburetor
throttle shaft. At all
times
vacuum in the chamber
is strong
enough
to overcome the tension of pump

diaphragm
spring. Upper pump spring serves as

a
bumper upon deceleration and as a delayed
action spring upon acceleration. Under any operat­ ing condition, when the pump diaphragm spring
overcomes vacuum in the chamber, the metering

rod
will
move
toward the wide throttle (power) position.

Note:
Nozzle is pressed in and should not be
removed.

E-16.
Metering Rod Adjustment

Check
metering rod adjustment each time the

carburetor
is reassembled. Before adjustment is
made, be sure that the flat of metering rod arm
is parallel to the flat of pump lifter
link
as shown
(Fig.
E-10.).
With
the throttle valve
seated
in
car­

buretor
bore, press down on the upper end of
diaphragm
shaft until the diaphragm
bottoms

in
the vacuum chamber. The metering rod should
now
seat
on casting with the metering rod
arm
flat against the pump lifter
link.
If the meter­
ing rod
does
not
seat
on the casting (check by 115

E

FUEL
SYSTEM
pressing downward on metering rod) or
seats
be­
fore the metering rod arm makes flat contact with the pump lifter link, make adjustment by bending
the lip on the metering rod arm.

E-17.
Choke System

The
choke system consists of a manually-operated
choke valve, a fast-idle connecting rod, and a fast-
idle arm. The choke valve is offset-spring loaded to prevent over-choking during the starting warm-
up period. When the choke valve is moved to a closed position for starting, the fast idle connector

rod
in Fig. E-ll revolves the fast idle link.
This
action increases the
engine
idle speed to prevent stalling during the warm-up period. A fast-idle
connector rod return spring prevents partial closing
of the choke valve. pump lifter which is connected to the throttle.

This
movement forces fuel from the chamber
above the diaphragm through discharge pump check valve and discharge pump jet.
This
auxiliary discharge of fuel supplies
engine
requirements for

quick
acceleration and heavy loads. When the
throttle is closed, the diaphragm is again pulled
down by high vacuum and another measured
charge of fuel enters the chamber above the
diaphragm
through the intake passage to be
available for the next cycle of operation.

Note:
The pump jet (see insert drawing in Fig.

E-12)
projecting into the air stream is permanently pressed into the carburetor body and should not
be removed. Also, carburetor design makes it im­ possible to adjust the pump stroke.
FIG.
E-ll—FAST
IDLE
ADJUSTMENT

1—Fast
Idle
Connector Rod
2—Fast
Idle
Link
E-18.
Fast
Idle Adjustment

With
the choke held in wide open position, lip (No. 1) (Fig.
E-ll)
on the fast-idle rod should con­
tact the
boss
on the body casting. Adjust by bend­
ing the fast-idle link at
offset
as shown by (No. 2).

E-19.
Accelerating Pump System

The
accelerating pump system shown in Fig. E-12
provides a measured amount of fuel for rapid acceleration and smooth
engine
operation when
the throttle is opened at lower speeds. In operation,
vacuum
is applied to the underside of diaphragm
at all times when the
engine
is running.
Lower

and
more uniform vacuum is provided by vacuum
restriction
and vacuum bleed passage. When the
diaphragm
is in its maximum down position at
low throttle resulting from high vacuum in chamber the chamber above the diaphragm is full of fuel

which
has been admitted through intake passage.
When
the throttle is opened, vacuum drops in the
chamber and the diaphragm is initially forced
upward
by the spring on the diaphragm shaft.
The
upward motion is picked up by accelerator
|
13347

FIG.
E-12—ACCELERATING
PUMP
SYSTEM

1—
Pump
Fuel
Passage
6—Intake
Passage

2—
Discharge
Pump Jet 7—Diaphragm

3—
Pump
Check
Valve
Ball
8—Vacuum Chamber 4—
Bail
Check
Weight
9—Vacuum
Restriction
Jet

5—
Pump
Lifter
Arm 10—Vacuum Bleed Passage
E-20.
Accelerating Pump Maintenance

If
engine
acceleration is unsatisfactory, remove the
pump diaphragm and check the diaphragm for wear

or
damage. Then remove the pump check retainer
ring
located directly above the pump check weight

and
pump ball check. Pump ball check must seat

properly
as a leak
will
cause poor acceleration performance. Inspect and replace all worn or
damaged parts.
Clean
and blow out all passages

with
compressed air.
Note
that when testing the pump for discharge volume with the carburetor
off the engine, only half of the maximum pump capacity
will
be discharged. When the
engine
is
operating, vacuum controls the balance of dis­ charge. 116

E

FUEL
SYSTEM
Note:
Do not remove pressed-in parts such as
nozzle, pump jet, or antipercolator air bleed.

j.
Remove body flange attaching screws, body flange assembly, and gasket.

k.
Remove idle-adjustment screw, spring, idle

port
rivet, throttle lever assembly, washer, fast
idle arm, throttle plate screws, throttle plate, and throttle shaft.
1. Remove throttle shaft seal by prying out seal

retainer.

Note:
Do not remove pressed-in vacuum passage

orifice.

m.
Remove choke valve screws and choke valve.

Unhook
choke spring and slide shaft from housing,
n.
Wash all parts in carburetor cleaning solution

and
blow out passages with compressed air. Do not immerse diaphragm or seals in cleaning solution.

Inspect
all parts for wear or damage. Always use
new gaskets when reassembling.

E-22.
Carburetor
Reassembly

•
Refer to Fig. E-13.

To
expedite
reassembly, it is advisable to group all

related
parts by the circuit to which they belong.

a.
Install
throttle shaft seal and retainer in flange casting.

b.
Install
fast-idle
arm,
washer, and lever assembly
on throttle shaft. Slide shaft into place and install throttle valve.

c.
Install
idle port rivet plug and idle adjusting

screw
and spring.

d.
Attach flange assembly to body casting. Use new gasket.
e.
Install
low-speed jet assembly.
f.
Early
production models install pump intake
strainer
in pump diaphragm housing and carefully
press into recess.

Note:
If strainer is even slightly damaged, a new
one must be installed.
g.
Install
pump diaphragm assembly in diaphragm housing.
Then,
install pump diaphragm spring
(lower)
and retainer.

h.
Install
pump lifter
link,
metering rod
arm,
upper
pump spring, and retainer.

I.
Install
metering rod jet.

Note:
No gasket is used with this jet.

j.
Install
diaphragm housing attaching screws in
the diaphragm housing, making sure that the

edges
of the diaphragm are not wrinkled.
Lower

into place and tighten screws evenly and securely,
k.
Install
throttle shaft seal, dust seal washer, and
shaft seal spring.

I.
Install
pump connector
link
in the throttle arm
assembly.
Install
throttle shaft arm assembly on
throttle shaft guiding connector
link
in pump lifter

link
hole.
CAUTION:
Linkage
must not bind in any throttle
position. If binding occurs,
loosen
clamp screw in
throttle arm, adjust slightly, then retighten screw.

m.
Install
pump check disc, disc retainer, and lock

ring.

n.
Install
metering rod and pin spring. Connect
metering rod spring.
o.
Check
and if necessary correct meter ing rod adjustment. Follow procedure of
Par.
E-16.
p.
Install
needle
seat and gasket assembly, needle,
float
and
float pin. The
stop
shoulder on the float
pin
must be on the side away from the bore of
the carburetor.

q.
Set float level to specifications. Follow pro­ cedure of
Par.
E-12.

r.
Install
air horn gasket and air horn assembly.

Install
attaching screws, lock washers, and choke
tube clamp assembly. Tighten center screws first,
s. Slide choke shaft and lever assembly into place
and
connect choke lever
spring.
Install
choke valve.
Center
the valve by tapping lightly, then hold in
place with fingers when tightening screws,
t.
Install
fast-idle connector rod with
offset
portion
of rod on top and pin spring on outside.
Install
fast-idle connecting rod spring.

E-23.
Correcting Acceleration
Flat
Spot

Early
production
Carburetor
Models 938-S, 938-
SA,
938-SC

Inasmuch
as a flat
spot
on acceleration or low speed
stumble can
come
from causes other than
car­

buretor
malfunction, it is recommended that
engine

tuning be thoroughly checked before attempting
any
actual carburetor work. Make sure that
ignition, compression, and timing are correct and
that fuel pump is supplying enough gas. Also, the F-head
engine
employs a water-heated intake

manifold.
Proper vaporization of the fuel depends
on correct intake manifold temperature. Since this
temperature is controlled by the cooling system
thermostat, include an operational check of the
thermostat when diagnosing the stumble. Operating
temperatures consistently below
155°F.
can cause stumble.

If
the stumble persists, a
YF-938-S,
YF-938-SA,

or
YF-938-SC
carburetor can be converted to a
YF-938-SD
carburetor by installing Special Kit
924161, consisting of a pump discharge check
needle, a metering rod, and a metering rod jet. If this kit is installed, the pump discharge check

needle
replaces the original
ball,
weight, and re­

tainer
and the small wire-type retainer used with
the
ball
check assembly must not be reinstalled.

When
installing the kit, check the size of the pump discharge jet, No. 2, Fig. E-14.
Early
production
YF-938S
and
YF-938SA
carburetors have a .025" [0,635 mm.] jet installed. If the carburetor being
converted has a .025" jet it must be opened up to .031" [0,787 mm.] by running a No. 68
drill
through
the jet as shown in
Fig.
E-14.
The jet must be drilled
as it is a pressed in part and cannot be replaced.
Upon
completing the installation of the conversion

kit,
mark
or tag the carburetor to indicate that it
is a
YF-938SD.
118

E

FUEL
SYSTEM
There
are six adjustments: curb idle speed, curb
idle mixture, float level, float drop, accelerator pump, and fast idle.
This
carburetor has six basic systems: float, low
speed, main metering, power, accelerator pump

and
choke.

E-26.
Float System

The
float system controls fuel level in the
car­

buretor fuel bowl. It maintains constant fuel level
to assure proper metering through all operating
ranges.

Fuel
enters the carburetor through the inlet screen
and
inlet valve. It flows past the valve
needle
and into the fuel bowl.
Fuel
continues to flow until

increasing
fuel level raises the float to a position
in
which it forces the inlet valve
needle
into its seat.
This
closes
the inlet valve. As fuel is used

from
the bowl, the float
moves
downward slightly.
This
allows the valve
needle
to
move
away from its
seat.
This
again allows fuel to enter the fuel bowl
to maintain fuel level. In this manner, float level maintains fuel level constant. See Fig. E-17. 12838

FIG.
E-17—FLOAT
SYSTEM
1—
Internal
Bowl
Vent
4—Float Tang

2—
Float
5—Float Needle
3— Needle
Pull
Clip
6—Needle
Seat

A
float prong, at the
rear
of the float arm
between

the float hangers, prevents the float from moving too far downward, yet allows it to
move
downward

far
enough to allow maximum fuel flow into the
bowl. A
pull
clip connects the float arm to the valve needle.
This
keeps the
needle
from sticking in the seat because of
dirt
or gum formation.

E-27.
Idle System

During
engine
idle operation, air flow through the

carburetor
venturi is very low. It is insufficient to
cause fuel to flow from the main discharge nozzles.
Therefore,
the idle system supplies fuel-air mixture

during
idle and low-speed operation.

The
idle system consists of the idle tubes, idle pas­

sages,
idle air bleeds, idle mixture adjustment
needles, off-idle discharge
slots
and idle discharge ports. See Fig. E-18.
FIG.
E-18—IDLE
SYSTEM

1—
Idle
Air Bleed 6—Throttle
Valve
2—
Idle
Air Bleed 7—Idle Needle
Hole

3—
Idle
Restriction
8—Adjustment Needles

4—
Lower
Idle
Restriction
9—Main
Metering
Jets
5—
Off
Idle
Discharge Port 10—Idle Tube
A—Throttle
Valve
in Off
Idle
Position
In
idle speed position, each throttle valve is slightly
open.
This
allows a small amount of air to pass

between
the carburetor bore
wall
and the throttle valve. Since there is not enough air flow for ven­

turi
action, manifold vacuum draws fuel directly

from
the fuel bowl through the idle system.

Fuel
from the float bowl passes through each main metering jet into the main well. A metered amount
of fuel flows through the idle tube restriction. It
then passes up the idle tube to a passage where

it
is mixed with air drawn through two calibrated
idle air bleeds.
Fuel-air
mixture then flows through

a
calibrated restriction into a vertical passage. It passes through another calibrated restriction to the off-idle discharge slot just above each throttle
valve.
This
injects additional air. It then flows
through the idle discharge port. The idle mixture
needle
controls the amount of fuel-air mixture

which
enters the carburetor bore at curb-idle posi­ tion of the throttle valve.

As
the throttle valve
opens
farther, more and more of the off-idle discharge slot is
exposed
to manifold
vacuum.
This
slot supplies additional fuel-air mix­
ture to
meet
off-idle
engine
requirements.

E-28.
Main
Metering System

As
the throttle valve continues to open, its
edge
moves
away from the carburetor bore
wall.
This
reduces vacuum applied to the idle discharge port
and
off-idle discharge slot, so that the idle system

ceases
to supply fuel-air mixture.

With
increased throttle opening, air velocity through the venturi increases.
This
causes a de­
crease of pressure in the carburetor bore, which is multiplied in the venturi. See Fig. E-19.
Since
the low air pressure (vacuum) is in the
venturi
at this time, fuel flows as follows:

Fuel
from the float bowl passes through the main metering jets into the main well and rises into the main well tubes. Air enters the main well through the main well air
bleeds
and mixes with 120

E

FUEL
SYSTEM
port into the venturi.

The
check
ball
in the pump plunger head is a vapor
vent for the pump well. Without this vent, vapor
pressure in the pump would force fuel from the
pump system into the
engine
manifold, causing

hard
starting when the
engine
is hot.
There
is another
hole
in the pump lever, into which
the accelerator pump rod can be inserted to pro­ vide quicker pump action.
This
adjustment setting
is used only in extreme cold temperature condi­ tions. The pump discharge check
ball
in the dis­
charge passage prevents discharge of fuel from the
pump nozzles when the accelerator pump is in­
operative.

E-31.
Choke System

The
choke system consists of a manually-operated
choke valve, a fast-idle connecting rod, and a fast-
idle arm. The choke valve is offset-spring loaded
to prevent over-choking during the starting
warm-
up period. When the choke valve is moved to a
closed position for starting, the fast idle connector

rod
revolves the fast idle
link.
This
action increases
the
engine
idle speed to prevent stalling during the

warm-up
period. A fast-idle connector rod return
spring
prevents
partial
closing of the choke valve.

E-32.
Carburetor
Removal

a.
Remove attaching wing nut and air cleaner from
carburetor.

b. Remove throttle cable from
ball
stud on throttle
lever adapter.

c.
Disconnect fuel line from carburetor inlet fitting.

d.
Disconnect positive crankcase ventilator
hose
from
nipple on carburetor body.
e. Disconnect distributor vacuum line from throttle body of carburetor.
f. Remove four attaching cap screws, carburetor,
and
gasket from intake manifold.

E-33.
Air
Horn
Body Removal and Disassembly

a.
Remove attaching screws, and carefully lift air
horn
body upward to remove from fuel bowl body.
b. Place air horn body in inverted position on
bench. Remove float hinge pin and lift float as­ sembly from cover. Remove inlet valve
needle
from
float arm. Remove
needle
seat, fiber gasket

and
seat screen from air horn body; discard gasket. See Fig. E-22.

c.
Depress shaft and allow spring to snap re­ peatedly to remove power piston from air horn body.
This
will
force power piston retaining washer

from
air horn body.

d.
Remove retainer from end of accelerator pump
plunger shaft. Remove pump assembly from pump

inner
arm. Loosen set screw on inner arm and re­

move
outer lever and shaft from plunger. Remove gasket from air horn body or fuel bowl body and

discard.

e. Remove two retaining screws and choke valve plate from choke shaft. Withdraw choke shaft from
air
horn body. Remove choke lever and collar from
choke shaft.
Note
position of choke lever in relation
12856
FIG.
E-22—AIR HORN BODY

1
—
Float

2— Power Piston
3—
Pump
Plunger
4—
Choke
Valve to choke trip lever at end of the choke shaft for

ease
in reassembly.

E-34.
Fuel
Bowl Body Disassembly

a.
Remove return spring of pump plunger and pump well from fuel bowl body. Remove small

aluminum
check
ball
from
bottom
of pump well
by inverting fuel bowl body and shaking into hand. Remove pump inlet screen from
bottom
of fuel bowl.
b. Remove main metering jets from fuel bowl body
using Tool C-3748.

c.
Remove power valve and fiber gasket from fuel bowl body; discard gasket.

d.
Remove three attaching screws, venturi cluster
assembly, and gasket from fuel bowl body. Center
screw has smooth shank and fiber gasket for the accelerator pump fuel bypass and seal.
e. Using a
pair
of long nosed pliers, remove T-
shaped retainer, accelerator pump discharge spring

and
steel discharge
ball
from fuel bowl body.
f. Remove two inserts from main well.

E-35.
Throttle Body Removal and Disassembly

a.
Invert
fuel bowl body; remove three attaching
screws,
throttle body and gasket; discard gasket.
b. Remove idle mixture adjustment
needles
and
springs from throttle body.

Note:
No further disassembly of the throttle body
is required. The throttle valves should never be
removed, as the idle and
spark
holes
are drilled in
direct
relation to the location of the throttle valves

and
shaft. Removal of the throttle valves
will
upset
this alignment. The throttle body assembly is serv­ iced only as a complete assembly with throttle valves intact.

E-36.
Carburetor
Cleaning and Inspection
Dirt,
gum, water, or carbon contamination on the 122