Boat help!

[smalleye]

I have a 2000 model 115 yamaha and it runs perfect when i change the plugs but after about 2 trips it only runs about half speed, and when i change the plugs i notice just one plug looks burnt up.I was just wondering if anyone would have any ideal what would cause this ? Thanks for any help

[Devils Horse]

Try changing just the one bad plug and see if that's the problem. If so you may have something wrong with either that cylinder or the ignition system. Either way I'd advise having it looked at soon or she may pop.

[cman]

Sounds like the carb for that cylinder is running to rich or too lean. A pretty easy job to take apart and rebuild if you're handy.
There are no fish in this pond

[dpage70]

completely clean plugs can also mean there's water getting in the cylinder. not trying to scare you but it's a possibility.

[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.

[tr186man]

If you are in the Louisville/Shephardsville area and want a mechanic to check it out, take it to Reynold's Performance Marine. Tony, the owner/mechanic is awesome. He is a Mercury guru but just about as good on Yamahas as well. I am not in no way associated with this business just a happy customer. I am very particular about how and what is done to all my mechanical devices (car, boat, lawnmower, etc.). So I am sure you will be satisfied with his work. It WILL run right when he gets done with it.