Yamaha YZ125X 2023, Owner'S Manual

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TROUBLESHOOTING
7-2
Incorrect idling speed or mid-to-high speed
Compression pressure is low
—
Measure the compression pres-
sure.
Loose spark plug
Tighten the spark plugs to the
specified torque.
Loose cylinder head or cylinder
Tighten bolts or nuts on cylinder
head and cylinder to the specified
torque.
Damaged cylinder head gasket Replace the cylinder head gasket.
Worn, damaged, or stuck piston
ring
Replace the piston and piston
rings as a set.
Seized or damaged piston
Replace the piston and piston
rings as a set.
Worn or damaged cylinder bore
Replace the cylinder, piston, and
piston rings as a set.
Symptom Possible cause Actions
Spark plug does not produce a
spark
Incorrect spark plug gap Adjust the spark plug gap.
Worn or damaged spark plug Replace the spark plug.
Defective spark plug cap Replace the spark plug cap.
Defective ignition coil Replace the ignition coil.
CDI unit failure Replace the CDI unit.
Fuel not supplied
Fuel leakage
Check the fuel passage. Repair or
replace as necessary.
Clogged carburetor fuel passage Clean the carburetor.
Clogged needle valve or needle
valve seat
Clean the needle valve or needle
valve seat.
Damaged float Replace the float.
—
Water or foreign material in fuel,
degraded fuel
Change fuel.
Clogged carburetor air passage Clean the carburetor.
Incorrectly adjusted throttle cable Adjust the throttle grip free play.
Incorrectly adjusted idling speed
(throttle stop screw)
Adjust the throttle stop screw.
Incorrectly adjusted pilot screw Adjust the pilot screw.
Incorrectly adjusted pilot air screw Adjust the pilot air screw.
Clogged pilot jet Clean the pilot jet.
Loose pilot jet
Tighten the pilot jet to the specified
torque.
Damaged or worn needle valve
seat
Replace the needle valve seat.
Loose needle valve seat
Tighten the needle valve seat to
the specified torque.
Symptom Possible cause Actions