Mercury Mariner 8/9.9HP 4-Stroke Factory Service Manual, Page 15Get this manual
Spark Plug Inspection Inspect spark plugs at the recommended intervals1Remove the spark plug leads by twisting the rubber boots slightly and pull off2Remove the spark plugs to inspect and cleanReplace spark plug if electrode is worn or the insulator is rough, cracked, broken, blistered or fouled3Set the spark plug gapSee Specification Chart in Section 1A4Before reinstalling spark plugs, clean away dirt on the spark plug seatsInstall plugs finger tight, and tighten 14 turn or torque to lbft(12.3 Nm)
Checking Engine Oil
IMPORTANT: Do not overfillBe sure that the outboard is upright (not tilted) when checking oil1Position the outboard vertical and remove the top cowl2Remove the oil level dipstickWipe the dipstick clean and reinsert it all-the-way in3Remove the dipstick and observe the oil levelIf the oil level is near or below the lower oil level (a), remove the oil filler cap (c) and fill to (but not over) the upper oil level (b) with the recommended oilPush the dipstick all the way back in when you're through4Reinstall the oil filler cap and tighten securely