TM 9-3431-254-14&P
To test for clogged fuel line, loosen fuel line nut at
TROUBLES - CAUSES AND REMEDIES
carburetor slightly. If line is open, fuel should drip
out at loosened nut.
Three prime requisites are essentia1 to starting and
maintaining satisfactory operation of gasoline en-
If the starter is `dead' or is unable to turn the engine
gines. They are:
over, check battery and cable connections at the bat-
tery, starting motor, and starting switch; also check
1. A proper fuel mixture in the cylinder.
for broken or frayed cables. Test starting switch and
2. Good compression in the cylinder.
starting motor and replace or repair if necessary.
3. Good spark, properly timed, to ignite the mixture.
COMPRESSION
If all three of these conditions do not exist, the en-
If the engine has proper compression, considerable
gine cannot be started. There are other factors which
resistance will be encountered in turning the engine
contribute to hard starting such as too heavy a load
over with the starting crank. If this resistance is not
for the engine to turn over at a low starting speed, a
encountered, compression is faulty. Following are
long exhaust pipe with high back pressure, etc. These
some reasons for poor compression:
conditions may affect starting, but do not necessarily
mean the engine is improperly adjusted.
Cylinder dry due to engine having been out of use for
As a guide to locating any difficulties which might
arise, the following causes are listed under the three
Loose or broken spark plug. In this case, a hissing
headings: Fuel Mixture, Compression, and Ignition.
noise will be heard in cranking engine, due to escap-
In each case, the causes of trouble are given in the
ing gas mixture on compression stroke.
order in which they are most apt to occur. If a remedy
Damaged cylinder head gasket or loose cylinder
is apparent, no remedy is suggested.
head. This will likewise cause hissing noise on
compression stroke.
STARTING DIFFICULTIES
Valve stuck open due to carbon or gum on valve stem.
FUEL MIXTURE
Valves adjusted with insufficient clearance under
No fuel in tank, shut-off closed or cap vent plugged.
valve stems. See `Valve Tappet Adjustment' Page B-17.
Fuel pump diaphragm worn out or punctured.
Piston rings stuck due to carbon accumulation.
Carburetor not choked sufficiently, especially if en-
Scored cylinders. This will require reboring the cy-
gine is cold. See `Starting Procedure', Page B-10.
linders and fitting with oversize pistons and rings,
Water, dirt, or gum in gasoline interfering with free
or replacement of complete cylinder barrels.
flow of fuel to carburetor.
IGNITION
Anti-diesel solenoid valve, at carburetor, inoperative.
No spark may be attributed to the following:
Check operation of valve A solenoid `click' should
be heard when ignition switch is turned to start
Ignition cable disconnected from coil, distributor, or
position. If not;
spark plugs. Cables wet.
Broken ignition cables, causing short circuits.
Check "for disconnected, loose or broken wire.
Remove solenoid from carburetor - clean plunger
and seat with solvent. Check plunger for spring
tension.
Replace solenoid valve if the above does not rectify
the problem.
Breaker points pitted or fused. Breaker arm sticking.
Poor grade or stale gasoline that will not vaporize
sufficiently to form the proper fuel mixture.
Carburetor flooded, due to excessive choking. See
ENGINE MISSES
Dirt or gum holding float needle valve in carburetor
Worn and leaking ignition cables.
open. This condition will be indicated if fuel conti-
nues to drip from carburetor with engine standing idle.
Weak spark or no spark in one of the cylinders.
Often, tapping the float chamber of the carburetor very
Loose connection at ignition cable.
lightly will remedy this trouble. Do not strike carbu-
retor with any metal tool.
Distributor breaker points pitted, worn or incorrect
If due to flooding, too much fuel entered the cylinder
in attempting to start the engine, the mixture will most
Water in gasoline.
likely be too rich to burn. In that case, starting may
be accomplished by continued cranking with the car-
buretor choke open.
Sticky valves.