Basic Troubleshooting
19
V. Makes unusual smoke when running.
a. Black smoke
, usually heavy, usually indicates a rich air fuel mixture.
• Not enough air: air flow blockage or a partially closed choke.
• Too much fuel: carburetor float or float valve stuck or metering / emulsion issues with the car-
buretor.
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 tipping. It can also be caused
by leaky carburetor float valve, if there is a down-hill path from the carburetor to the intake port.
Check oil for gasoline smell, repair carburetor.
c. Blue smoke,
usually light.
PCV system.
• May be blocked or unplugged.
• May be over-come by massive over-filling or oil dilution with gasoline.
• Will cause oil to exit the engine via any low-resistance paths.
Piston rings.
• Confirm with leak-down test.
• Smoke will be more pronounced under load.
• Repair may not make economic sense.
Valve guides (and intake valve stem seal).
• Smoke will be more pronounced on over-run.
VI. 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 coming into play as the engine
RPMs cross the activation threshold. This will have no ill effects on engine performance.
• Half-engine speed clatter: loose valve lash.
• Half-engine speed clatter, slightly heavier: wrist-pin.
• Rhythmic heavy-light engine speed click: piston slap.
c. Spark-knock
• Advanced ignition timing.
• Low octane fuel.
• Over-heating engine (check for blocked cooling air flow).
• Carbon build-up in cylinder: glowing carbon chunks pre-igniting air fuel mix.
d. Chirp
• Compression, blowing-by the fire-ring of a damaged head gasket will sometimes produce a
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