Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionWiring Diagram (Other than US, CA and CAL without KIBS Models)
ZX1000JC
ZX1000JD
...
Safe riding technique
The points given below are applicable for everyday motorcycle use and
should
be carefully observed for safe and effective vehicle operation.
For safety, eye protection and a
helmet are strongly recommended.
You should be aware of and verify
the applicable safety regulations in
force prior ...
Cylinder (Upper Crankcase) Wear Inspection
Split the crankcase (see Crankcase Splitting).
Remove the pistons (see Piston Removal).
Assemble the cylinder (upper crankcase) [A], the cylinder
head [B] and the cylinder head gasket [C].
Tighten the cylinder head bolts (see Cylinder Head Installation
in the Engine Top End chapter).
...