2017 Merc 383. Can tell it's running rich just from the smell, noticed some wiffs of smoke out the exhaust at idle as well. Seems off.

Oil pressure looks goodBoat idles fineIn and out of gear fine
starts right up and no odd sounds
WOT rpm is off about 200 from what it was about 2 months ago but I also nicked the prop a bit so guessing that's it coupled with a non waxed bottom from previous 5200 rpm wot. I need to pull a plug I guess and see how it looks. But not sure what I can check myself without getting a Mercury scan gauge or having a tech look at it.

I also feel like on a few WOT runs the boat would start to lose speed but rpms stayed the same until I brought them down. Trimmed all the way out on flat calm water not sure if it's related but wanted to mention it.

Pulled the air filter off and the throttle body is clean as a whistle.




Not sure if I'm chasing an issue or just my imagination.

Pull all the plugs and inspect them. Easy peasy.

Check plugs for oil. I am guessing you may have some bad valve seals. I had one not too long ago have the same issue, it eventually dropped 2 valve seats....might be worth pulling the exhaust manifold to take a look before it is too late.

x 2.
Do compression test all 8 while they are out. Also do fuel psi test and look up to see what it should be , for reference.

yes , pull the exh manifolds and check the heads