the pump and the supply tanks. The trouble might be
caused by a clogged fuel line strainer or by an air leak
in the line. If the wobble pump is pumping, the trouble
may be in the line to the engine fuel pump or in the
engine fuel pump itself.
Check the fuel lines for cracks, dents, loose
connections, sharpbends, andclogging. You can remove
the fuel line at the pump and use air to determine if the
line is open.
Check fuel pumps for leaks at the pump gaskets or
in the fuel line connections. Check fuel pump filters or
sediment bowl screens for restrictions. Check the bypass
for operation. If the bypass valve is defective, replace
the fuel pump. In diaphragm-type fuel pumps, the filter
bowl gasket, the diaphragm, or the valves may be the
source of trouble. Check for air leaks in the diaphragm
by submerging the discharge end of the fuel line in
gasoline and looking for air bubbles while cranking the
engine. If the engine will run, a leaky diaphragm is
indicated by gasoline leakage from the pump air vent.
Carburetor trouble may be the cause if fuel does not
reach the cylinders. You can check this by removing the
spark plugs and looking for moisture. If there is no trace
of gasoline on the plugs, the carburetor may be out of
adjustment, the float level may be too low, or the jets
may be clogged. If the fuel level in the carburetor float
bowl is low, the float valve is probably stuck on the seat.
If the fuel level in the float is correct, yet no fuel is
delivered to the carburetor throat, the carburetor will
have to be removed, disassembled, and cleaned.
Faulty ignition system parts may be the source of
starting difficulties. You may encounter two kinds of
ignition systems-the MAGNETO type and the
BATTERY type. Even though the parts of these systems
differ in some respects, their function is the same;
namely, to produce a spark in each cylinder of the engine
at exactly the proper time in relation to the position of
the pistons and the crankshaft. Also, the system is
designed so the sparks in all cylinders follow each other
in proper sequence.
ENGINE FAILS TO STOP
If a gasoline engine fails to stop when the ignition
switch is turned to the OFF position, the trouble is
usually caused by a faulty ignition circuit, improper
timing, the octane rating number of the fuel being too
low for the design of the engine, or the engine being
overheated.
In a magneto-type ignition system, an open ground
connection may cause an engine to run after the ignition
switch is turned off. When a magneto ground connection
is open, the magneto will continue to produce sparks as
long as the magneto armature magnets rotate, and the
engine will continue to run. In other words, when the
magneto ignition switch contact points are closed, the
ignition should be SHUT OFF. This is not true of the
booster coil circuit of a magneto-type system, nor of the
usual battery-type ignition system. In these systems, an
open ground or open switch points prevent current flow.
If the switch of a battery-type ignition system fails to
stop the engine, the contact switch points have probably
remained closed.
If the ignition switch and the circuit are in good
condition, failure to stop may be caused by overheating.
If the engine is overheated, normal compression
temperature may become high enough to ignite the fuel
mixture even though no spark is being produced in the
cylinders. When this happens in a gasoline engine, the
engine is, in reality, operating on the diesel principle.
Normally, you will detect the symptoms of
overheating before the temperature gets too high. The
causes of overheating in a gasoline engine are much the
same as those for a diesel engine.
Other troubles and their symptoms, causes, and
corrections that may occur in a gasoline engine are
similar to those found in a diesel engine. Troubles
leading to the loss of rpm, irregular operation, unusual
noises, abnormal instrument indications, and excessive
consumption or contamination of the lube oil, fuel, or
water can usually be handled in the same way for
gasoline and diesel engines. Of course, there are always
exceptions, so it is best to consult the manufacturer’s
technical manual.
Most gasoline engines in the Navy are used by shore
activities. Afloat, gasoline engines are used to drive
portable pumps like the P-250, a piece of fire-fighting
and dewatering equipment. Although pumps like the
P-250 are primarily maintained by members of the
Damage Controlman (DC) rating, Enginemen are
involved to some extent in repairing or overhauling the
P-250.
Before you disassemble a P-250 for repair, make
sure that all the repair parts are available and on hand.
When repairs are not within your ship’s force capability,
you must turn the unit in to an IMA or SRF for repair.
Attach an OPNAV 4790/2K (work order form) to the
pump. Figure 3-45 illustrates a typical P-250 pump unit.
3-45
