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PART 10-1-
GENERAL FUEL SYSTEM SERVICE
10-5
CARIURETTOR DIAGNOSIS GUIDI (Continued)
INCONSISTENT ENGINE
IDLE SPEED
AUTOMATIC CHOKE
SLOW WARM-UP
I
ON
TOO OnEN
SEVERE TRANSMISSION
ENGAGEMENT AnER
COLD ENGINE START
SURGING (CRUISING
SPEEDS TO TOP SPEEDS)
REDUCED TOP SPEED
TESTS
FUEL PUMP TESTS
Two tests: fuel pump static pres-
sure and fuel volume are necessary
to determine that the fuel pump is in
satisfactory condition.
If both the fuel pump volume and
pressure are within specifications
(pagel0·76) and the pump and lines
are in satisfactory condition, a vac-
-
uum test is not required.
If the pump volume is low, but
the pressure is within specifications,
a fuel pump capacity test must be
made with the in-line filter, if fitted,
High fuel level or float setting.
Fuel inlet needle not seating prop-
erly or worn needle and/ or seat.
Malfunctioning automatic choke.
Excessively dirty air cleaner.
Fast idle screw contacting low
step of cam at curb idle.
Sticking carburettor throttle shaft.
Excessive looseness of throttle
shaft in bores of throttle body.
Incorrectly
installed
throttle
plates.
Thermostatic choke setting too
rich.
Choke linkage sticking or binding.
Incorrect choke linkage adjust-
ment.
Choke phite misaligned or binding
in air
.
horn.
Carburettor fast idle
speed setting
too high.
Throttle operating on starting step
Clogged main jet
Improper
size
main jet
Low fuel level or float setting.
Low fuel pump pressure or vol-
ume.
Clogged fuel filter or carburettor
Float setting too high or too low.
Fuel pump pressure or volume too
high or too low.
Improper size or obstructed main
jet
.
Power valve spring weak,
or
power valve restricted.
Restricted air bleeds.
removed. If the pump volume meets
specifications with the filter removed,
replace the filter. If the pump vol-
ume is still below specifications,
repeat the capacity test, using an
auxiliary fuel supply. If the pump
volume still does not meet specifica-
tions, replace the pump. If the pump
does meet specifications, there is a
restriction in the fuel supply from
the tank or the tank is not venting
propedy.
The tests are performed with the
fuel pump installed on the engine
and the engine temperature stabi-
Worn or damaged main metering
jet.
Accelerating
pump
Elastomer
valve (Motorcraft 2-V/4-V
carburet-
tors). Ball check and/or weight not
seating properly.
Incorrect throttle linkage adjust-
ment to carburettor.
Binding or sticking throttle link-
age or accelerator pedal.
Idle compensator malfunctioning
(if so
equipped).
Positive crankcase ventilation sys-
tem restricted.
Sticking fuel inlet needle.
Defective power valve or gasket.
Defective coolant thermostat.
Restriction or air leak in the
choke vacuum or hot air
passage.
Choke heat inlet tube
restricted.
Choke clean air tube restricted.
(highest step) of the fast idle cam.
Binding or sticking throttle link-
age
.
filter
screen.
Distributor
clogged.
vacuum
passage
Restriction in main fuel passages.
Excessive dirt in air cleaner.
Throttle plate(s) not fully
open.
Faulty choke operation.
Improper throttle linkage adjust-
ment.
lized at the normal operating tem-
p_
erature. Make certain the re-
placeable fuel filter is not rest-
ricted or clogged. When in doubt,
install a new fuel filter prior to per-
forming the tests. A clogged or
restricted filter is often the cause of
fuel system malfunction.
Pressure Test
1. Remove the carburettor air
cleaner assembly (page 10·67
).
Dis-
connect the fuel inlet hose at the fuel
filter. Unscrew the filter from the
carburettor. Connect the fuel hose to
the filter and tighten the retaining
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