the pump and the supply tanks. The trouble might becaused by a clogged fuel line strainer or by an air leakin the line. If the wobble pump is pumping, the troublemay be in the line to the engine fuel pump or in theengine fuel pump itself.Check the fuel lines for cracks, dents, looseconnections, sharpbends, andclogging. You can removethe fuel line at the pump and use air to determine if theline is open.Check fuel pumps for leaks at the pump gaskets orin the fuel line connections. Check fuel pump filters orsediment bowl screens for restrictions. Check the bypassfor operation. If the bypass valve is defective, replacethe fuel pump. In diaphragm-type fuel pumps, the filterbowl gasket, the diaphragm, or the valves may be thesource of trouble. Check for air leaks in the diaphragmby submerging the discharge end of the fuel line ingasoline and looking for air bubbles while cranking theengine. If the engine will run, a leaky diaphragm isindicated by gasoline leakage from the pump air vent.Carburetor trouble may be the cause if fuel does notreach the cylinders. You can check this by removing thespark plugs and looking for moisture. If there is no traceof gasoline on the plugs, the carburetor may be out ofadjustment, the float level may be too low, or the jetsmay be clogged. If the fuel level in the carburetor floatbowl is low, the float valve is probably stuck on the seat.If the fuel level in the float is correct, yet no fuel isdelivered to the carburetor throat, the carburetor willhave to be removed, disassembled, and cleaned.Faulty ignition system parts may be the source ofstarting difficulties. You may encounter two kinds ofignition systems-the MAGNETO type and theBATTERY type. Even though the parts of these systemsdiffer in some respects, their function is the same;namely, to produce a spark in each cylinder of the engineat exactly the proper time in relation to the position ofthe pistons and the crankshaft. Also, the system isdesigned so the sparks in all cylinders follow each otherin proper sequence.ENGINE FAILS TO STOPIf a gasoline engine fails to stop when the ignitionswitch is turned to the OFF position, the trouble isusually caused by a faulty ignition circuit, impropertiming, the octane rating number of the fuel being toolow for the design of the engine, or the engine beingoverheated.In a magneto-type ignition system, an open groundconnection may cause an engine to run after the ignitionswitch is turned off. When a magneto ground connectionis open, the magneto will continue to produce sparks aslong as the magneto armature magnets rotate, and theengine will continue to run. In other words, when themagneto ignition switch contact points are closed, theignition should be SHUT OFF. This is not true of thebooster coil circuit of a magneto-type system, nor of theusual battery-type ignition system. In these systems, anopen ground or open switch points prevent current flow.If the switch of a battery-type ignition system fails tostop the engine, the contact switch points have probablyremained closed.If the ignition switch and the circuit are in goodcondition, failure to stop may be caused by overheating.If the engine is overheated, normal compressiontemperature may become high enough to ignite the fuelmixture even though no spark is being produced in thecylinders. When this happens in a gasoline engine, theengine is, in reality, operating on the diesel principle.Normally, you will detect the symptoms ofoverheating before the temperature gets too high. Thecauses of overheating in a gasoline engine are much thesame as those for a diesel engine.Other troubles and their symptoms, causes, andcorrections that may occur in a gasoline engine aresimilar to those found in a diesel engine. Troublesleading to the loss of rpm, irregular operation, unusualnoises, abnormal instrument indications, and excessiveconsumption or contamination of the lube oil, fuel, orwater can usually be handled in the same way forgasoline and diesel engines. Of course, there are alwaysexceptions, so it is best to consult the manufacturer’stechnical manual.Most gasoline engines in the Navy are used by shoreactivities. Afloat, gasoline engines are used to driveportable pumps like the P-250, a piece of fire-fightingand dewatering equipment. Although pumps like theP-250 are primarily maintained by members of theDamage Controlman (DC) rating, Enginemen areinvolved to some extent in repairing or overhauling theP-250.Before you disassemble a P-250 for repair, makesure 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 thepump. Figure 3-45 illustrates a typical P-250 pump unit.3-45
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