Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 308Get this manual
Maintenance Instructions Maintenance inspection is owner's responsibility and must be performed at intervals specified, following:
Normal ServiceEvery 50 hrsof operation or 60 days (whichever comes first) Severe ServiceEvery 25 hrsof operation or 30 days (whichever comes first)
Operation in salt water area is considered "Severe Service
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