If the starter motor and battery are in good operating condition but the starter fails to crank the engine, the trouble will usually be in the drive connection between the motor and the ring gear on the flywheel. Troubles in the drive assembly are usually in the form of broken parts or a slipping clutch (if applicable). A slipping clutch may be the result of the engine not being free to turn or of the clutch not holding up to its rated capacity. Even though seldom encountered, a stripped ring gear on the flywheel may be the source of trouble if the starter motor does not turn the engine.

ENGINE CRANKS BUT FAILS TO START

Starting troubles and their causes and corrections may vary to some degree, depending on the particular engine. If the prescribed prestarting and starting procedures are followed and a gasoline engine fails to start, the source of trouble will probably be improper priming or choking, a lack of fuel at various points in the system, or a lack of spark at the spark plugs. Improper priming may be either underpriming or overpriming. Priming instructions differ, depending on the engine. Information on priming also applies to engines equipped with chokes. A warm engine should never be primed. Some engines may require no priming except when they are started under cold weather conditions.

On some installations, underpriming can be checked by the feel of the primer pump as it is operated On other installations, underpriming may be due to insufficient use of the choke.

Over-priming is undesirable because it results in a flooded engine and makes starting difficult. It also causes excess gasoline to condense in the intake manifolds, run down into the cylinders, wash away the lubricating oil film, and cause pistons or rings to stick You can determine flooding by removing and inspecting a spark plug. A wet plug indicates flooding. If you find the engine to be flooded, be sure to dry out or deflood it according to prescribed instructions. Some installations specify that the ignition switch must be ON, while others state the switch must be OFF; therefore it is important for you to follow the engine manufacturers instructions.

Improper carburetion may be the source of trouble if a gasoline engine fails to start. On some engines a check of the fuel pressure gauge will indicate whether lack of fuel is the cause. If the gauge shows the prescribed pressure, the trouble is not lack of fuel; if the gauge shows little or no fuel pressure, you should check the various parts of the delivery system to locate the fault.

In some installations, you can determine whether the trouble is in the gauge or in the fuel system by using the following procedure: (1) remove the carburetor plug next to the fuel pressure gauge connection; and (2) use a suitable container to catch the gasoline, and operate the pump used to build up starting fuel pressure. If fuel is reaching the carburetor, gasoline will spurt out of the open plug hole; this indicates that the gauge is inoperative. If no fuel flows from the plug opening, the trouble is probably in the fuel system somewhere between the fuel tank and carburetor. Even though all installations do not have a fuel pressure gauge, the procedure for checking the fuel system is much the same.

If a wobble pump is installed to build up starting fuel pressure, you can determine whether the pump is operating correctly by the feel and sound of the pump. If the pump feels or sounds dry, the trouble is between 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.