TM 5-3895-359-14&P
scored too severely, an entirely new cylinder block may
Poor grade or stale gasoline that will not vaporize
be necessary.
sufficiently to form the proper fuel mixture.
IGNITION
Carburetor flooded, caused by too much choking
especially if engine is hot.
See 'Magneto Ignition Spark' No spark may also be
attributed to the following:
Dirt or gum holding float needle valve in carburetor
open.
This condition would be indicated if fuel
Ignition cable disconnected from magneto or spark
continues to drip from carburetor with engine standing
plugs.
idle. Often tapping the float chamber of the carburetor
Broken ignition cables, causing short circuits.
very lightly with the handle of a screw driver or similar
Ignition cables wet or soaked.
tool will remedy this trouble. Do not strike carburetor
with any metal tools, it may cause serious damage.
Spark plug insulators broken.
Also if the mixture in the cylinder, due to flooding, is too
Spark plugs wet or dirty.
rich, starting may be accomplished by continued
Spark plug point gap wrong.
cranking, with the carburetor choke open.
Condensation on spark plug electrodes.
If, due to flooding, too much fuel should have enter, ed
the cylinder in attempting to start the engine, the mixture
Magneto points pitted or fused.
will most likely be too rich to burn. In that case, the
Magneto breaker arm sticking.
spark plugs should be removed from the cylinders and
Magneto condenser leaking or grounded.
the engine then turned over several times so the rich
mixture will be blown out through the spark plug holes.
Spark time wrong. See 'Magneto Timing'
The choke oil the carburetor should of course be left
ENGINE MISSES
open during this procedure. The plugs should then be
Spark plug gap incorrect. See 'Spark Plugs'.
replaced and starting tried again.
Worn and leaking ignition cables.
To test for clogged fuel line, loosen fuel line nut at
carburetor slightly. If line is open, fuel should drip out at
Weak spark. See 'Magneto Ignition Spark'.
loosened nut.
Loose connections at ignition cable.
COMPRESSION
Magneto breaker points pitted or worn.
If the engine has proper compression, considerable
Water in gasoline.
cranking resistance will be encountered.
If this
Poor compression. See 'Compression'
resistance is not encountered, compression is faulty.
Following are some reasons for poor compression:
ENGINE SURGES OR GALLOPS
Cylinder dry due to engine having been out of use for
Carburetor flooding.
some time. See 'Restoring Compression '.
Governor spring hooked into wrong hole in lever. See
Loose spark plugs or broken spark plug. In this case a
'Governor Adjustment' Governor rod incorrectly
hissing noise will be heard when cranking engine, due to
adjusted. See 'Governor Adjustment'.
escaping gas mixture on compression stroke,
ENGINE STOPS
Damaged cylinder head gasket or loose cylinder head.
Fuel tank empty.
This will likewise cause hissing noise on compression
stroke.
Water, dirt or gum in gasoline.
Valve stuck open due to carbon or gum on valve stem.
Gasoline vaporized in fuel lines due to excessive heat
To clean valve stems, see 'Valves' Valve tappets
around engine (Vapor Lock). See 'Stopping Engine'.
adjusted with insufficient clearance under valve stems.
Vapor lock in fuel lines or carburetor due to using winter
See 'Valve Tappets'.
gas (too volatile) in hot weather.
Piston rings stuck in piston due to carbon accumulation.
Air vent hole in fuel tank cap plugged. Engine scored or
If rings are stuck very tight, this will necessitate
stuck due to lack of oil.
removing piston and connecting rod assembly and
Ignition troubles. See 'Ignition'
cleaning parts. See 'Piston and Connecting Rod'.
ENGINE OVERHEATS
Scored cylinders. This will require reboring of the
cylinders and fitting with new pistons and rings. If
Crankcase oil supply low. Replenish immediately.
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