Yamaha F115 won't maintain WOT

[Yamauser]

My Yamaha F115TXRA had the high pressure fuel pump replaced. It also had an issue of water in the fuel. Both the canister and the small filter were replaced and as much water removed from the gas tank as possible. Now it runs great up to about 2800 rpms. The throttle can be punched and it will run at WOT for a few seconds and then cut off. It can be restarted and does the same thing. The mechanic water tested it with a portable tank and it still did the same thing. He even tried pumping the bulb to maintain fuel pressure. Does this still sound like a fuel problem or should he be looking at something else? Master Techs from now on.

 

[capt sam]

Re: Yamaha F115 won't maintain WOT

did he clean out the fuel system or the injectors, did you replace the fuel?

 

[Yamauser]

Re: Yamaha F115 won't maintain WOT

After they "removed" the water, I topped it off with fresh gas and pumped about a quart of gas with the bulb to make sure the fresh gas had gotten through. They also said they cleaned the injectors.

 

[Casco Bay Outrage]

Re: Yamaha F115 won't maintain WOT

What year is your motor and how many hours?

Why was the high pressure fuel pump replaced? What was the symptom?

What RPM is WOT for your boat?

When you say "cut out" is that "stall" or run rough.

Can you advance the trottle to 4000 and cruise? If so for how long? What about cruising at 5000 and 5500?

You need to get rid of all the water.

I learned from Rodbolt, you need to look at the entire fuel system.

As for the engine, there are several items before the injectors. Replace both low and high pressure fuel filters.

Drain and clean the VST. To do this you need to pull off the intake manifold.

Where the injectors sent out to a professional shop for cleaning and bench testing? If not, they could still be a cause.

We need you to give us more information on what the symptoms are, when they happen and when they don't.

 

[Yamauser]

Re: Yamaha F115 won't maintain WOT

The motor is an 02. I have no idea how many hours it has. The high pressure fuel pump was replaced because it was dead, it would not run even when hooked directly to a battery. It won't cruise above about 2800. It will go to wot, 6000 for a few seconds then it stops. Can you tell me more about the VST? I must be confusing it with the visible fuel filter on the side of the engine block. Where would the high pressure and low pressure fuel filters be located? Thanks

 

[Casco Bay Outrage]

Re: Yamaha F115 won't maintain WOT

Here is what happened to me.

Bogging down thread

The VST is a tank mounted on the inside of the intake. Do you have a service manual?

Here are the general locations of the filters.

The high pressure filter is cartridge and inside a black housing on the fuel line. It is not a mounted cartridge.

 

[Yamauser]

Re: Yamaha F115 won't maintain WOT

Thanks Casco. I found the vst filter in a shop manual drawing. I copied that page for my mechanic. I could not find the inline fuel filter in the shop manual. I copied your picture and will give that to the mechanic also. If this doesn't do it, I will just have to cut my loses and start with a new mechanic.

 

[rodbolt]

Re: Yamaha F115 won't maintain WOT

the A model 115 did not use an inline filter between the lift pump and the VST.
its also not a high pressure filter.
its reccomended to cut one in and yamaha sells one with fuel line and all for 60 bucks or so.
its a 10 micron pre-filter.
the VST pump has a tiny screen that can clog and give that exact symptom.
each injector has a fine screen of about 10 micron as well that can clog.
sounds like the cylinders,or at least one, is simply running out of fuel.
possible causes, clogged restricted system between the liquid level in the tank and the engine fuel filter. debris in the lift pump,debris in the VST or debris in an injector.

 

[Yamauser]

Re: Yamaha F115 won't maintain WOT

Thanks for the reply Rodbolt. The mechanic tells me he did clean the VST tank, which was full of gunk, and the screen before the first sea trial. Today he pulled it again and found the filter to be clogged with rust particles. He is going through the entire fuel system again. Shouldn't the new 10 micron spin-on filter catch any additional water?

 

[ChriSarasota]

Re: Yamaha F115 won't maintain WOT

Just a post for future reference.
2006 f115 - 80hrs. on a Hurricane GS 190. We usually can squeeze out about 5900rpm/36mph
Well maintained, clean, covered and started regularly...but hadn't been out and seen an open throttle in about 8 months.
I had the same problem where the motor started and ran fine, up to about 3/4 throttle and then fell down to about 3500 any time full throttle was applied.
The first thought was bad gas, so we got some new spark plugs and hooked the motor to a 6 gallon belly tank and took it for a spin. We got a couple hundred more rpm, but were still bogging down at or near WOT.
I dug through some great information here and was able to begin trouble shooting under the assumption it must be the VST filter or an injector.
Being that it's in new condition, and the separator and sight cup are visibly very clean, we decided that it's more likely to be gum or varnish than it is physical debris. so, we hooked it up to the 6-gallon belly tank with a bottle of fuel injector cleaner in it...(follow the label and the professionals...might not be a good idea, but it worked for this one guy, this one time)
By the time we idled from the dock to the channel, it was already gone. the first hole shot was as good as new and we were off to the races. Ran the snot out of 4-5 gallons, hooked it back to the old gas in the old tank and rand the snot out of 20 more gallons.
We're back in business...4 dollars later!
Thank you so much for offering your professional knowledge to help like-minded people!

Innerwebz roxorz!

 

[rodbolt]

Re: Yamaha F115 won't maintain WOT

if it had not of worked,and it rarely does. you most likly would be posting about a hole in a piston or burned ex valves as thats what lean running does.
PLEASE folks DO NOT attempt a snake oil in a can treatment.
it can lead to catastrophic failures.
its even worse with two stroke motors damage happens very quickly on them.

 

[ChriSarasota]

Re: Yamaha F115 won't maintain WOT

Point well taken, and the advice greatly appreciated.
Thanks again for spending the time to not only gain the knowledge and experience, but to share it as well.

We were at least able to blossom from S.O.Luck to Dumb Luck.
Next step, halfway informed decisions!
...can't say thank you enough...so, thank you.