02' Yamaha F115 - slight miss at times?

[311Hemi]

I just bought a boat a few months ago with a 2002 Yamaha F115 and the engine runs pretty good, always starts right away and idles fine. If I rev it up for a few seconds when cold (right after it's started) and back off quickly it will die, but once it's warm no issues.

When it comes to engines the smallest little details of an engine not running quite right are always in my head. After using the boat for a week in Canada last week I am noticing what seems to be a slight miss when I am running anywhere from 1500-3500 RPMs, more noticeable towards the lower end of that range. It runs fine for the most part, but I can tell just slight hick-up's in RPMs and you can ever so slightly feel it in the boat also when it does it and it. Many people might not even notice it. I can see the tack move very slightly when it's doing this also (almost not noticeable), which seems more often than not it is usually doing it. It also seems to idle a bit rough at times, almost like it's idling just a tad lower than it should. Not very often but once in a while when I go from idle to WOT to move to another fishing location (basically getting up on plane) I will get slight hesitation for a second but it will recover right away and then power up smoothly to WOT and runs great WOT.

The guy said the tank was full of gas (from last season) when I bought it and that it was stabilized. I have since ran through about 30 gallons and have put 1/2 can of Seafoam in it.

I pulled the plugs today and noticed all four plugs are fairly carboned up, is this normal? I don't know when they were last changed but will be doing that this week.

I also pulled the fuel filter on the engine and noticed a little sediment in the bowl, and after I let the gas from the bowl sit for a bit I noticed a little water had accumulated. Is there anything I can do (seafoam, etc) to try to rid the tank of any moisture/water? Pretty sure seafom will do that but I don't know if it will remove all of it.

Thoughts?

[broken_line]

try out new spark plugs..

[311Hemi]

Yep, doing that first.

I will also be doing a ring-free shock treatment. I don't think the previous owner ran any ring free, at least he never mentioned it.

[Northlander]

I was going to suggest ring free. If that dont work take it in.

[Surface Tension]

Change your plugs but to the ring free first.

I'd take a sample of the gas and flush the fuel line too.

Jack up the tongue all the way. Let the boat rest there.

The hose can act like a trap from the bends and elevation.

Get the outlet of the hose low, and depress the outlet valve while having someone squeeze the primer bulb. Pump gas into a glass jar.