Yamaha YZ 2020 Series, Owner'S Service Manual, Page: 348 / 376

TROUBLESHOOTING
9-3
Excessive noise from engine
—
Worn camshaft lobe Replace the camshaft.
Water or foreign material in fuel,
degraded fuel
Change fuel.
Contaminated throttle body or
clogged internal passage
Clean the throttle body.
Incorrectly adjusted throttle cable Adjust the throttle grip free play.
Incorrectly adjusted idling speed
(idle screw)
Adjust the idle screw.
Incorrect throttle position sensor
angle
Adjust the throttle position sensor
angle.
Incorrect acceleration position
sensor angle
Adjust the acceleration position
sensor angle.
Faulty ECU Replace the ECU.
Clogged vacuum hose Clean the vacuum hose.
Cracks and damage in vacuum
hose
Replace the vacuum hose.
Damaged throttle body joint Replace the throttle body joint.
Loose throttle body joint
Tighten the throttle body joint bolts
to the specified torque.
Clogged air filter element
Clean or replace the air filter ele-
ment.
Incorrect oil level (high)
Adjust the oil level to the specified
level.
Symptom Possible cause Actions
Noise heard from around cylinder
head
Incorrect valve clearance (too
wide)
Adjust the valve clearance.
Fatigued or broken valve spring Replace the valve spring.
Worn or damaged camshaft lobe Replace the camshaft.
Worn or damaged valve lifter
Replace the valve lifter and cylin-
der head as a set.
Worn or damaged camshaft jour-
nal
Replace the camshaft.
Worn or damaged cylinder head
(camshaft journal)
Replace the cylinder head.
Noise heard from around timing
chain
Worn or damaged timing chain
Replace the timing chain and cam-
shaft sprocket as a set.
Worn or damaged camshaft
sprocket
Replace the timing chain and cam-
shaft sprocket as a set.
Worn or damaged timing chain
guide
Replace the timing chain guide.
Cracked, damaged, or faulty tim-
ing chain tensioner
Replace the timing chain ten-
sioner.
Symptom Possible cause Actions