Fuel pump diaphragm worn out or damaged.
Carburetor not choked sufficiently, especially if engine is cold. See 'Starting Procedure', Page 9.
Water, dirt, or gum in gasoline interfering with free flow of fuel to carburetor.
Poor grade or stale gasoline that will not vaporize sufficiently to form the proper fuel mixture.
Carburetor flooded, caused by too much choking especially if engine is hot. See 'Starting Procedure'.

Dirt or gum holding float needle valve in carburetor open. This condition should be indicated if fuel continues to drip from carburetor with engine standing idle. Often tapping the float chamber of the carburetor very lightly with the handle of a screw driver or similar tool will remedy this trouble. Do not strike carburetor with any metal tool.

If due to flooding, too much fuel entered the cylinder in attempting to start the engine, the mixture will most likely be too rich to burn. In that case the spark plug should be removed and the engine turned over several times with the starting sheave, so the rich mixture will be blown out through the spark plug hole. The choke must be left open during this procedure. Spark plug should be dried off, assembled, and starting tried again.

COMPRESSION
Beginning with engine Serial No. 4225490, these models of engines were provided with an automatic compression release, so that the normal method of detecting faulty compression, by the resistance encountered when turning the engine over on the compression stroke, no longer holds true.

Check the following for suspected lack of compression, if the fuel and ignition systems are not the cause of starting difficulties and loss of power.

IGNITION
See 'Ignition Spark', Page 11. No spark may also be attributed to the following:

Ignition wires disconnected from magneto, coil, spark plug or breaker box.
Broken ignition wires causing short circuits.
Spark plug cable wet or oil soaked.
Spark plug insulator broken. Plug wet or dirty.
Spark plug point gap wrong. See Page 15.
Breaker points pitted or fused.
Breaker arm sticking.
Condenser leaking or grounded.
Oil in breaker box. See 'Crankcase Breather', Page 11.
Spark timing wrong. See 'Timing', Page 12.

ENGINE MISSES
Spark plug gap incorrect. See Page 15.
Worn and leaking ignition cable.
Weak spark. See 'Ignition Spark, Page 11.
Loose connections at ignition wires.
Breaker points pitted or worn.
Oil in breaker box. See 'Crankcase Breather'. Page 11
Water in gasoline.
Poor compression. See 'Compression', Page 17.

ENGINE SURGES OR GALLOPS
Carburetor flooding.

Governor spring hooked into wrong hole in lever, or governor rod incorrectly adjusted. See 'Governor Ad- justment', Page 25.

ENGINE STOPS
Fuel tank empty. Water, dirt or gum in gasoline.

Gasoline vaporized in fuel lines due to excessive heat around engine (Vapor Lock). See 'Stopping Engine', Page 9.

Vapor lock in fuel lines or carburetor due to using winter gas (too volatile) in hot weather.

Cylinder dry due to engine having been out of use. See 'Restoring Compression', Page 16.

Loose or broken spark plug. In this case a hissing 'noise will be heard in cranking engine due to escaping gas mixture on compression stroke.

Damaged cylinder head gasket or loose cylinder head. This will likewise cause hissing noise on compression stroke.

Valve tappets with insufficient clearance under valve stems. See 'Tappet .Adjustment', Page 24.

Valve stuck open due to carbon or gum on valve stem. To clean valve stems, see 'Valves and Seat Insert'. Page 19.

Piston rings stuck in piston due to carbon accumulation. This will require removing piston and connecting rod assembly, and cleaning parts. -See 'Connecting Rod and Piston'. Page 22.

Scored cylinder. This will require reboring the cylinder and fittings with new piston and rings. If scored too severely an entirely new cylinder block may be necessary.

TESTING OF REBUILT ENGINE
An engine that has been completely overhauled, such as having the cylinder rebored and fitted with new piston, rings and valves, should go through a thorough "run-in" period before any load is applied to it.

The engine should be started and allowed to run for about one-half hour, at about 1600 to 1800 R.P.M. without load. The R.P.M. should then be increased to engine operating speed, still without load, for an additional three and one-half to four hours.

The proper "running-in" of the engine will help to establish polished bearing surfaces and proper clearances between the various operating parts.

DRAIN OIL FROM CRANKCASE
BEFORE DISASSEMBLY

ACCESSORIES
Remove muffler and disconnect ignition wire from spark plug. If engine is to be completely overhauled, remove all accessories.

On engines equipped with a combination motor-generator; disconnect wires and adjusting strap at the generator. Remove bracket and motor-generator from side of crankcase as a complete unit.

Caution: In reassembly, do not put too much tension on drive belt.

FUEL TANK (Fig. 21)
Close fuel valve at tank and disconnect fuel line. Remove three nuts and washers which hold tank bracket to cylinder head studs. Fuel tank and bracket can then be removed as a complete unit.

Tighten the capscrews of the cylinder head, gear cover, connecting rod, stator plate and the spark plug to the specified torque readings indicated in the paragraphs of reassembly, relative to these parts.

While the engine is partly or fully dismantled, all parts should be thoroughly cleaned. Use all new gaskets in reassembly and lubricate all bearing surfaces.

The following procedure is for complete disassembly of an engine. Instructions on reassembling are also given, as often it will not be necessary to disassemble the entire engine. As disassembly progresses, the order may be altered somewhat, as will be self-evident to the mechanic.

CARBURETOR and AIR CLEANER (Fig. 22)
The carburetor and air cleaner should be removed both to facilitate working on the engine and to prevent damage to these parts. Unscrew wing nut and remove air cleaner. Be careful of oil in cleaner. Disconnect; breather line at inspection cover, throttle rod clip at governor lever and fuel line. Take out the two nuts holding carburetor flange to cylinder, and remove carburetor - air cleaner bracket as a complete unit.