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Discussion Starter #1
So I have a Yamaha f115 2014 model with 280 hours on it. For some reason one day all of a sudden my motor started doing bad at idle. Kinda rough and sometimes would shut off when slowing down from cruising speed. When I got back from fishing I went to go load the boat and now it won’t stay running. It starts great fires great but no idle. Dies 2 seconds after starting.

Talked to a couple people and they said change your primer bulb so I did that because it had never been changed and it was easy. Still nothing...

Changed the battery connections, battery, even the cables and still nothing. So I think there is a fuel/air problem somewhere that I am not finding.
Thanks in advance!!!
 

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What make boat? Assuming it's a built in tank and prolly an anti back flow valve.

Sent from my XT1585 using Tapatalk
 

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I would say dirt in your fuel idle Solenoid system. Try putting a concentrated bottle of StarBright..Bought at Walmart... straight into your Fuel/water seperator filter. Unscrew it...Pour some gas out and put the WHOLE bottle into the Fuel Water Seperator Filter then carefully screw it back on..Start engine..Should SHOCK the system and clean out any debris or dirt that is in your Idle Solenoid system.
 

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Did you change your fuel water separators? Possibly the VST tank. If your bulb ducks flat then anti siphon valve as the other member posted. I am betting fuel related
 

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There is a list of easy things to check first, but when I had a similar issue, it was the tiny filter in the V.S. Tank (vapor stabilization tank). It wasn't dirty, but had a white chalky crust across the screen. I have a 2008.
Shipoke
 

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Discussion Starter #6
Just changed the separator that wasn’t that old. Still no change. I’m guessing the VST is behind the intake manifold like in some of the videos I looked up???
 

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I’m guessing the VST is behind the intake manifold like in some of the videos I looked up???

Yes its is. The first time i went after the VST, it took 4 hours..... now its an annual PM to check the VST
screen, and takes 1-2 hours max........you can do it. Even if its not the problem, you will know how to eliminate
potentials.
Shipoke
 

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I would say dirt in your fuel idle Solenoid system. Try putting a concentrated bottle of StarBright..Bought at Walmart... straight into your Fuel/water seperator filter. Unscrew it...Pour some gas out and put the WHOLE bottle into the Fuel Water Seperator Filter then carefully screw it back on..Start engine..Should SHOCK the system and clean out any debris or dirt that is in your Idle Solenoid system.
Do you mean sea foam?
 

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Discussion Starter #9
Just ordered the VST filter. Gonna change it and hopefully that fixes the problem. After much research I’m feeling confident that is the problem. I’ll let everybody know when I finish.
 

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I had had similar issue it was a low compression cylinder. Check all your plugs for excessive oil or damage
 

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Discussion Starter #12
So I replaced the VST filter and that definitely seemed to help. The filter was very dirty and needed to be changed. I started the motor and at first it wouldn’t stay running but I thought that was because I de-primed the fuel system. Then I got it primed up and it finally would run on its own at idle and sounded good. Not great but definitely better. So I looked into the spark plugs. They were all evenly worn and all burnt pretty good so I decided to go ahead and change them. Good compression in all cylinders.

Now... the problem still exists but only when starting the motor. When starting, the motor will go up and down in RPMS multiple times before either stalling out or leveling out to a good idle. Either way I can get it running fine now but I know it’s not idling/starting correctly still. Any more advice???

The only thing I haven’t changed is the small fuel filter on the front of the motor because I would have to order it.

thanks again!!
 

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Discussion Starter #13
My next thought is going to be drain the fuel (maybe it’s bad fuel) and treat and refill the whole system.
 

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Does Yamaha have an IAC sensor? If so, I'd be very suspect of that.
 

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I'd get a separate 1 gallon fuel tank/can/bucket or whatever, and mix the appropriate amount of seafoam for 1 gallon fuel, then run it thru the engine while running in idle. If your vst filter was that nasty and gummy, I'd suspect the fuel lines and carbs are nasty too. Let the seafoam clean it for you, especially the low idle needle valve, it may be just sticking.
 

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The F115 has a spot you can hook a fuel pressure gauge to it at the top of the fuel rail. Once you turn the key the electric fuel pump comes on and produces approximately 38-40psi at the rail. (That pressure figure is from memory may want to verify specs)

You can ihook up and use the gauges to get a pressure reading while underway. The pressure should be a consistent 38-40 psi (again check that figure as it’s from memory and it’s been several years since I looked up the spec)

If the fuel pressure reading at the rail is low you have a dirty filter or clogging issue somewhere back from the fuel rail. Or possibly a bad electric fuel pump...doubt that though cause of the low hours.

If the fuel pressure is good at the rail your injectors may be dirty clogged with that same stuff that was in the vst. DAPs auto up near 29 And old paradox used to clean injectors for a good price. There is a place called flagship marine where you can send your injectors and they will give you a graph that shows flow through the injector...

if you have good fuel, and good fuel pressure measured at the rail and clean injectors your problem is most likely not in the fuel system....

By the way you should be able clean and reuse the vst filter many times before it needs to be replaced.
 

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On my 2008, is an inline filter between the little filter (the one in the pic above) and the VST. It is encased in a rubber boot that makes it hard to see. Your newer model may not have it, but look for it any way. Also, years ago i began using a 2 micron filter instead of the Yamaha 10 micron. Its a Racor S3220SUL. Its built for a clear , screw on bowl that you will need to buy the first time. Not a local item....get on line.
Shipoke
 

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On my 2008, is an inline filter between the little filter (the one in the pic above) and the VST. It is encased in a rubber boot that makes it hard to see. Your newer model may not have it, but look for it any way. Also, years ago i began using a 2 micron filter instead of the Yamaha 10 micron. Its a Racor S3220SUL. Its built for a clear , screw on bowl that you will need to buy the first time. Not a local item....get on line.
Shipoke
Was not aware of that filter. If you have the time, could you snap a picture of it so I can see if any of mine has one? Thanks Shipoke.
 

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H20MARK:
Look for item #34 in the "FUEL INJECTOR PUMP" pic. It lays next to the fuel rail in a rubber boot, which will be directly after the fuel pump. Keep in mind, this is an 08. I have helped other 115 owners with their fuel issues and the 08 is the only year i have seen that has it.
Shipoke
 
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