Chapter 2: Basic Troubleshooting
14
V. Low compression
a. Check valve lash
b. Check compression
c. Check leak down to identify the
source of the compression loss.
VI. Flow blockage
A. Exhaust blockage, usually accompanied by
an unusual exhaust sound.
• Just as a throttle on the carburetor
controls the engine RPMs by limit-
ing the amount of air an engine
can breath in, an exhaust block-
age will limit engine performance
by constricting the other end of the
system.
• The muffler itself may be blocked.
• The exhaust valve may not be
opening fully, possibly because of
extremely loose valve lash set-
tings.
• The exhaust valve seat may have
come loose in the cylinder head.
This may cause a loss of compres-
sion, a flow blockage or it may ran-
domly alternate between the two.
NOTE: The cause of an exhaust valve coming
loose is usually over heating.
B. Intake blockage
• An intake blockage up-stream of
the carburetor will cause a rich
fuel/air mixture and constrict the
amount of air that the engine can
draw in, limiting performance.
NOTE: A blocked air filter is a common cause of
this.
• The intake valve not fully opening.
A possible cause of this is loose
valve lash.
C. Makes unusual smoke when running
a. Black smoke, usually heavy usu-
ally indicates a rich air fuel mixture
• Not enough air: air filter blockage
or a partially closed choke.
• Too much fuel: carburetor float or
float valve stuck or metering /
emulsion issues with the carbure-
tor.
b. White smoke, usually heavy
• Oil in muffler, usually the result of
improper tipping. the engine will
“fog” for a minute or so, then clear-
up on its own.
• Massive oil dilution with gasoline.
It may be caused by improper tip-
ping. It can also be caused by
leaky carburetor float valve, if
there is a down-hill path from the
carb. to the intake port. Check oil
for gasoline smell, repair carbure-
tor.
c. Blue smoke, usually light.
1 PCV system
• May be blocked or unplugged.
• May be over-come by massive
over-filling or oil dilution with gaso-
line.
• Will cause oil to exit the engine via
any low-resistance paths.
2Piston rings
• Confirm with leak-down test.
• Smoke will be more pronounced
under load.
• Repair may not make economic
sense.
3 Valve guides (and intake valve
stem seal).
• Smoke will be more pronounced
on over-run.
A. Makes unusual noise when running
a. Knock
• Check for loose mounting of
engine or driven implement
• Rotate crankshaft back-and-forth
to check for loose connecting rod.
b. Click
• Clicks and pops on engine shut-
down: Compression release com-
www.mymowerparts.com
For Discount White Outdoor Parts Call 606-678-9623 or 606-561-4983
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