05 Yamaha F115 - Still losing power

[tomn3]

I've had a performance issue going on over a month now. Started a while back when I went WOT. Went to 5400 rpm then fell back and stalled. Started right back up and was able to take it slowly up to over 4K. Kept it low until we made it back. Prior to this the motor ran like a champ.(BTW-new to me, very lightly used)
After that took it to the Yamaha tech. Cleaned the VST, compression test(good) and fuel pressure checked out. Was able to get it up to 5K after that. Then it slowly started losing rpm's each trip.

Checked the fuel vent, opened the cap, etc No effect. Had the fuel tank pumped and cleaned.
Went tubing once and had fun but never got over 4k.

Tried tubing again and it died at 3k, had to limp back to the dock.

I was about to buy a test tank and the tech said 90% of the time it's injectors. So I sent them off for cleaning.
Put them in and ran it this evening. Sounded very smooth and quiet. Planed nicely at 3-3500 rpm. But wouldn't go over 4200. Ran a while, backed off to slow speed and tried again. This time it only made 3k and fell back, sputtering worse than ever.

Sorry for the long post.

Any ideas next? Low pressure fuel pump? Get a test tank to isolate the boat?

Thanks for any help.

 

[tomn3]

Re: 05 Yamaha F115 - Still losing power

One other thing....when the mechanic serviced and cleaned the VST his report says "hooked up pressure gauge, seems ok, pressure jumping around at idle". I should have questioned that at the time but didn't. Does this maybe point to something going bad? When he took it on a sea trial after he says he ran it up to 5K, again I should have asked but was that it? It wouldn't go higher?...

thanks,

 

[99yam40]

Re: 05 Yamaha F115 - Still losing power

monitor the fuel pressures/vacuum as that will give you some idea of what is going on and yes you should have pushed the tech farther and he should have done more testing

 

[tomn3]

Re: 05 Yamaha F115 - Still losing power

Thanks yam,

I'm not a mechanic but can do some of the work. How exactly do you monitor the pressure under way? Pull the cowl off and hook up to the fuel rail before leaving the dock? Should it maintain a steady pressure throughout?
I'm at a marina and while convenient for some things I have to run 15 minutes to get out of a Manatee zone, so testing each time is kind of a pain.

Thanks