Sick Yamaha F115

[MSRiverdog]

2001 115 Four Stroke seems short on power, runs smooth until about 3900 then sounds almost like the rev limiter is trying to kick in, when cool isn't as bad but still gutless. Runs at 4500 to 5500 sometimes. New plugs, gas and fuel filter, ran Yamaha ring free and it helped over what it sounded like before. About 300 hrs a year, any thoughts or ideas before my bringing it in?

[BRUNO]

Had a sick Johnson that acted like that as well. Ran fairly good when cold. Stop and restart and it mumbled and grumbled its' way accross the lake. Turned out that one of the cylinders had a tripped or faulty temp sensor that threw the motor into limp mode. Great American in Bloomington fixed it.

[MSRiverdog]

Thanks for the come back BRUNO.

Took it out today for about 6 hours and it ran from like the outer day to very good. Sometimes it seemed if I tried to slosh around the gas, quick stop and start, it would run better for at least a minute or two.

[Valv]

I would suspect something electronic too. Sound like your motor is going in fault/limp mode.

How's the water cooling ?

[PierBridge]

Do You use a fuel/water separator (?? micron)?

If You do not use such separator chances are it could be the injectors that are not clean (enough) but that is only a guess.

I do not know how fine filters can be used in a fuel/water separator but 10 micron filter is rather common (I have that on my F115). I'm talking about an external fuel/water separator, like this:

Link

If the injectors are suspected I do not think You can clean them Yourself, a professional probably need to do it (but I do not think You need to buy new in such case).

I would also check the spark plugs are OK (correct make and model plus correct gap) and that it is actually spark on all plugs.

A compression test on all cylinders could also be a good thing to perform. Just the easy things first.

What prop do you use (diam x pitch)?

What is max RPM at full throttle (when it runs OK)? 5500 RPM? It should be preferebly close to 6000 RPM.