Honda CRF230F 2004 Owner's Manual page 187

Quick Reference
The following is a brief, but important
collection of information you need to know
about your Honda. You'll also find space to
record important notes.
Quick Reference
How To Avoid Costly Repairs
The engine of your Honda can be the most
expensive component to repair. Proper
maintenance, especially the use of the
recommended fluids and filters, prevents
premature wear and damage.
Frequent causes of costly engine repairs are:
Engine oil: insufficient quantity, improper
oil.
Air cleaner: dirty, leaking because of
improper installation (poor seal).