TM 55-4920-381-13&P
cylinders and fitting with new pistons and rings. If
Carburetor not choked sufficiently, especially if en-
scored too severely, an entirely new cylinder block
gine is cold.
may be necessary.
Water, dirt, or gum in gasoline interfering with free
flow of fuel to carburetor.
IGNITION
Poor grade or stale gasoline that will not vaporize
See `Magneto ignition Spark', Page 12. No spark may
sufficiently to form the proper fuel mixture.
also be attributed to the following:
Carburetor flooded, caused by too much choking,
Ignition cable disconnected from magneto or spark
especially if engine is hot. Crank with choke open.
plugs.
Dirt or gum holding float needle valve in carburetor
Broken ignition cables, causing short circuits.
open. This condition would be indicated if fuel con-
Ignition cables wet or oil soaked.
tinues to drip from carburetor with engine standing
idle. Often tapping the float chamber of the carbu-
Spark plugs wet or dirty.
retor very lightly with the wood handle of a screw
Spark plug point gap wrong. See Page 14.
driver or similar instrument will remedy this trouble.
Do not strike carburetor with any metal tools, it may
Condensation on spark plug electrodes.
cause serious damage. Also if the mixture in the
Magneto breaker points pitted or fused
cylinder, due to flooding, is too rich, starting may be
accomplished by continued cranking with the carbu-
Magneto breaker arm sticking.
ret or choke open.
Magneto condenser leaking or grounded.
If, due to flooding, too much fuel should have enter-
Spark timing wrong. See 'Magneto Timing', Page 13.
ed the cylinder in attempting to start the engine, the
mixture will most likely be too rich to burn. In that
ENGINE MISSES
case the spark plugs should be removed from the cyl-
inders and the engine then turned over several times
Spark plug gap incorrect. See Page 14.
with the starting crank, so the rich mixture will be
Worn and leaking ignition cables.
blown out through the spark plug holes. The choke
on the carburetor should of course be left open during
Weak spark. See `Magneto Ignition Spark', Page 12.
this procedure. The plugs should be dried off, reas-
Loose connections at ignition cable.
sembled, and starting tried again.
Magneto breaker points pitted or worn.
To test for clogged fuel line, loosen fuel line nut at
carburetor slightly. If line is open, fuel should drip
Water in gasoline.
out at loosened nut.
Poor compression. See `Compression', Page 15.
COMPRESSION
ENGINE SURGES OR GALLOPS
If the engine has proper compression, considerable
Carburetor flooding.
resistance will be encountered in the pull on the
Governor spring hooked into wrong hole in lever, or
starting crank. If this resistance is not encountered,
governor rod incorrectly adjusted. See `Governor Ad-
compression is faulty. Following are some reasons
justment', Page 22.
for poor compression:
Cylinder dry due to engine having been out of use for
ENGINE STOPS
some time. See `Restoring Compression', Page 14.
Fuel tank empty.
Loose spark plugs or broken spark plug. In this case,
a hissing noise will be heard in cranking engine, due
Water, dirt or gum in gasoline.
to escaping gas mixture on compression stroke.
Gasoline vaporized in fuel lines due to excessive
Damaged cylinder head gasket or loose cylinder head.
heat around engine (Vapor Lock). See `Stopping E n -
This will likewise cause hissing noise on compres-
gine', Page 11.
sion stroke.
Vapor lock in fuel lines or carburetor due to using
Valve stuck open due to carbon or gum on valve stem.
winter gas (too volatile) in hot weather.
To clean valve stems, See `Valves', Page 20.
Air vent hole in fuel tank cap plugged. Engine scored
Valve tappets adjusted with insufficient clearance
or stuck due to lack of oil.
under valve stems. See `Valve Tappets', Page 21.
Ignition troubles. See `Ignition', Page 15.
Piston rings stuck in piston due to carbon accumula-
tion. If rings are stuck very tight this will necessitate
ENGINE OVERHEATS
removing piston and connecting rod assembly and
cleaning parts. See `Piston and Connecting Rod',
Crankcase oil supply low. Replenish immediately.
Page 19.
Ignition spark timed wrong. See `Magneto Timing',
Page 13.
Scored cylinders. This will require reboring of the
D-15
