I have a 1985 Mercury 90 hp inline v6 outboard . I went out yesterday and it ran fine all day at its usual 38-40mph until I started it up to run back down the lake to go home . It started fine ,idled fine ,but when i hit the throttle it felt real boggy and did a whopping 9mph back to the ramp.

We pulled off the cover and checked the plugs . The top 3 were bone dry and the bottom 3 had oil on them. Cleaned them off and went back out and it ran fine again , back up to its usual 38-40mph.

It wasnt smoking alot or anything even when running bad. I always mix exactly 50-1 like it says.

Anyone have any ideas why bottom 3 plugs could get oil and other 3 are fine? And what I could do to fix this.  Plugs were replaced in fall of last year and look brand new. Would a fuel filter help?

I had an 85 merc 90 on a 16' boat, it lost power like yours a couple of times then all the time it ended up being the power pack. There's one for each 3 cyl.