2003 ST 4 Stroke 9.9/15HP Johnson outboards Service Manual, Page 38Get this manual
PERIODIC MAINTENANCE BREATHER AND FUEL LINE
BREATHER AND FUEL LINE
Inspect initially after 10 hours (1 month) and every 50 hours (3 months) thereafter Replace every yearsIf leakage, cracks, swelling or other damage is found, replace
FUEL FILTER
Inspect every 50 hours (3 months) Replace every 400 hours or yearsIf water accumulation, sediment, leakage, cracks, or other damage is found, replace