Troubleshooting
15
•
Too much fuel: needle valve stuck or metering / emulsion issues with the carburetor.
b. Blue smoke, usually light.
•
Too much oil in the fuel mix.
IX.
Piston rings
a. Confirm with compression test.
b. Repair may not make economic sense.
X.
Makes unusual noise when running.
•
Knock
*
Check for loose mounting of engine or driven implement
*
Rotate crankshaft back-and-forth to check for loose connecting rod.
•
Click
*
Half-engine speed clatter, slightly heavier: wrist-pin.
*
Rhythmic heavy-light engine speed click: piston slap
•
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.
XI.
Unusual exhaust tone
a. Splashy, blatty, wheezing or whistling.
•
Splashy or blatty idle usually indicates a slightly rich condition.
•
Whistling or wheezing may indicate an exhaust blockage, usually slightly muffled.
•
Backfire
*
On over-run: unburned fuel igniting past exhaust port. Mixture not burning completely in
combustion chamber. It may be too rich or it may be a spark plug or an ignition problem.
•
Skip
*
Usually ignition related.
NOTE:
If the engine is run with no load at maximum RPMs, the rev limiter may be triggered causing the engine
to skip at 7,900 RPM. This is a normal function of the rev limiter.
*
Run the engine with a spark tester in-line between the spark plug wire and the spark plug
or use an oscilloscope and see if the spark goes away at the same time the engine dies.
XII. Engine RPMs surge (hunting)
a. The Ideal stoichiometric ratio/AFR (Air Fuel Ratio) for this engine is (12.5:1 - 13:1). An engine
that runs with an AFR greater than 13:1 is running lean. The engine RPMs will sink until they
reach a point that can be supported by the available fuel. This causes a momentary surge in
power until the available fuel is consumed, then the RPMs fall again, repeating the cycle.
•
Too much air: look for an air leak in the intake tract
•
Not enough fuel: look for fuel supply or carburetor problems
For Parts Call 606-678-9623 or 606-561-4983
www.mymowerparts.com
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