Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionEngine Sprocket Removal
Remove:
Engine Sprocket Cover Bolts [A]
Engine Sprocket Cover [B]
Flatten out the bended washer [A].
Remove the engine sprocket nut [B] and washer.
NOTE
When loosening the engine sprocket nut, hold the rear
brake on.
Raise the rear wheel off the ground with the stand. ...
Crankcase Halves Assembly
Install:
Crankshaft (see Crankshaft Installation)
Connecting Rods (see Connecting Rod Installation)
Using a cleaning fluid, clean off any oil or dirt on the mating
surface of the crankcase halves.
Apply liquid gasket to the mating surface of the lower
crankcase half as shown in the fi ...
Air Cleaner Element Replacement
NOTE
In dusty areas, the element should be replaced more
frequently than the recommended interval.
WARNINGIf dirt or dust is allowed to pass through
into the
throttle body assy, the throttle may become stuck,
possibly causing accident. Replace the air cleaner
element according ...