Boat help!

[MarkW]

Please give a little better definition of "burned up" Is the tip actually melted, or is it just a different color or is it oily? All these things are a indication of what's going on. I would do a compression test of every cylinder, making notes on each one so you know which cylinder is the weakest and strongest. Also, I would have to have each carb checked--especially the one with the problem plug. It could end up causing engine damage real fast, if you are not careful and get this fixed.
Ooops---I assumed it was carbed. Is is injected or carbureted? If it's injected---you may have an injector problem.

[smalleye]

I changed the plugs then took it out and it ran fine for like two trips, then i changed the plugs and noticed the one looked just a little black and the others looked fine, it's not melted or oily just a little black,and i changed them again and it ran fine for another trip or so, and now it's back to running bad, this is all over about a month period. i had ngk plugs in it before this and it seemed to do ok , and i couldn't find any ngk plugs so i went and bought some champions from walmart until i could find some better plugs. Does anybody know what yamaha recomends(sp), and as far as compression goes i had it checked right before this and the guy that checked it said it was good. thanks for any help because i am a mechanical idiot.

[CTFSHWHISKER]

Go back to ngk plugs,my dad has an xr4 merc and my uncle has a 225 yammaha,they will not run on champion plugs and i saw this happen may times on 2cycle lawm equipment when i was reparing them.