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1()..4
GROUP 10-
FUEL SYSTEM
CARIUREnOR DIAGNOSIS GUIDE-continued
STAUING
ROUGH IDU
POOR
ACCELERATION
ENGINE HOT OR COLD
Incorrect idle fuel mixture.
Engine idle speed too slow (fast
or cold idle adjustments).
Dirt, water or ice in fuel filter.
Positive crankcase ventilation sys-
tem malfunctioning.
Fuel lines restricted or leaking air.
Fuel tank vent restricted.
Leaking intake
manifold or car-
burettor gaskets
Carburenor icing (cold, wet or
humid weather).
Incorrect throttle linkage adjust-
Positive crankcase ventilation sys-
tem malfunctioning or restricted.
Idle air bleeds restricted.
Idle air or fuel passages restricted.
Idle discharge holes restricted.
Idle discharge holes not in proper
relation to throttle plate(s).
Excessive dirt in air cleaner.
High or low fuel level or float set-
ting.
Fuel inlet needle not seating prop-
erly, or worn needle or
seat.
Power valve leaking.
Restricted air bleeds.
Poor acceleration complaints fall
under one of three headings: the en-
gine is sluggish on acceleration, the
engine stalls when accelerated, or
the engine hesitates or develops a flat
A
LEAN
MIXTURE
ON
ACCELERATION
CAN IE
CAUSED
IY:
Low fuel pump pressure.
Sticking fuel inlet needle.
Low fuel
le~l
or float setting.
Restriction in main fuel passage.
Air leak between the carburettor
and the manifold caused by loose
mounting bolts or defective gasket.
Air leak at the throttle shaft
caused by a worn throttle shaft.
Accelerating pump diaphragm de-
fective.
Incorrect
accelerating
pump
stroke adjUstment.
A RICH MIXTURE ON
ACCELERATION
CAN IE
CAUSED IY:
Excessive fuel pump pressure.
ment to carburettor.
Clogged air bleeds or idle pas-
sages.
Defective fuel
pump.
ENGINE HOT ONLY
Coolant control thermostat defec-
tive.
Excessive looseness of throttle
shaft in bore(s) of throttle
body.
Incorrect idle mixture adjustment.
Idle adjusting needle(s) grooved,
worn, or otherwise damaged.
Plugged idle fuel channel restric-
tor.
Worn or damaged main metering
jet.
Accelerating pump discharge ball
check and/ or weight not seating
properly.
Fuel pump pressure too low, or
excessive.
Restriction in main fuel passage.
spot when accelerated. Poor acceler-
ation is caused by either an exces-
sively lean or rich mixture on ac-
celeration and/ or defects or improp-
er adjustments in the ignition system.
Accelerating pump fuel inlet valve
(Elastomer valve or ball check-
Motorcraft
2-V/4·V
carburettors) not
seating on acceleration.
Restriction in the accelerating
pump discharge passage.
Accelerating pump discharge Elas-
tomer valve (Motorcraft
2-V/4-V
car-
burettors) ball check or weight not
coming fully off its seat, or failing to
seat properly on the reverse stroke of
the pump
diaphragm.
Air leak at the accelerating pump
cover caused by a defective gasket
or warped pump cover.
Incorrect accelerating pump stroke
adjustment.
Power valve leakage.
Restricted air bleeds.
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