# Yami 115 4 stroke issues



## texasag07 (Nov 11, 2014)

2011 Yamaha 115 4 stroke.

Boat will run like normal sometimes for a couple miles then, then looses power hard and almost tosses you from boat at higher speed, then power will come back on suddenly then it will kinda surge a couple times if you let it do it’s deal it runs shitty but normally stays running. 

If you just idle it will run all day with no issues.

Most times I will put in neutral and I can then take off again after 30 seconds or so, most times it won’t go far after I have done this before stuttering or problem persists.

If I pump the primer bulb which most times I can pump 2-4 times before it get harder. I can resume operation for sometimes 1 minute sometimes 10. It seems slightly better at anything under 4K rpms.

At one point the first day it did this I pulled the fuel filter after it shutdown and it was almost empty so I then replaced the primer bulb. I forgot to pull the filter again yesterday when it started running bad to see if there was fuel in the filter. Since you can pump the ball im betting it is still not full.

Also seems to get worse the hotter the engine gets.

Things I have ruled out:
Water in fuel- I drained the tank and replaced fuel filter, refilled w seafoam and some Heet water reducer magic potion. I set some of the fuel from tank drain into a clear container and it had possibly a slight haze to it versus fresh gas but nothing horrible and not defined separation of fuel and water. Skiff gets ran just about every weekend. No change.

Replaced primer bulb- as the first day it did this I pulled the fuel filter off once it shutdown and there was almost no fuel in the filter. Seemed better but not near right.


Things I am thinking could be wrong.
Dirty or clogged injectors
Bad low pressure fuel pump
Dirty vst
Some sort of fuel line blockage

Thoughts?

Plugs changed, injectors cleaned, and high pressure fuel pump replaced 6-8 months ago.


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## Smackdaddy53 (Dec 31, 2012)

Sounds like either collapsed inner wall on the fuel line or bad fuel pump. Fuel line is cheap, I’d start there and rebuild the fuel pump.


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## Guest (Nov 19, 2018)

Ok, I’ll take a stab too!
Sounds like fuel problem to me too!
Go to hardware store and get 1-2’ clear hose the same diameter or real close to your fuel line and a double barb. This doen’t have to be expensive stuff as it’s only for diagnosis. Install clear hose as close to motor as possible, prime fuel system and run boat like normal. Look for air in the clear hose as you run it. Any air bubbles after a minute of running and you have a leak allowing air in. You can also install a vacuum gauge inline to check for restriction.


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## Smackdaddy53 (Dec 31, 2012)

Boatbrains said:


> Ok, I’ll take a stab too!
> Sounds like fuel problem to me too!
> Go to hardware store and get 1-2’ clear hose the same diameter or real close to your fuel line and a double barb. This doen’t have to be expensive stuff as it’s only for diagnosis. Install clear hose as close to motor as possible, prime fuel system and run boat like normal. Look for air in the clear hose as you run it. Any air bubbles after a minute of running and you have a leak allowing air in. You can also install a vacuum gauge inline to check for restriction.


He could also try running the motor off a remote gas tank and see how she runs to eliminate the fuel system from the tank to the motor.


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## DONAGHUE (Nov 18, 2017)

Check your fuel tank vent...


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## texasag07 (Nov 11, 2014)

As an update I pulled everything apart and checked/cleaned the injectors/vst. Injectors were clean and clear and the vst screen was about 20-30% clogged. 

Also replaced the fuel line from the tank to the fuel/water filter/separator.

Between these two she is back up and running.


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## MariettaMike (Jun 14, 2012)

That’s Good news.

It was probably the old fuel hose clogged or collapsing at higher flow rates.

Sometimes you can just blow the clog out with air versus replacing.

If the problem comes back you should try removing the anti-siphon valve from your fuel tank.

90% of outboard problems are fuel system related.


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## sjrobin (Jul 13, 2015)

The Yamaha F series have three fuel filters under the cowling. Also need to use the Yamaha injection cleaner with every fuel addition. I had a air gap between the primary screw on fuel filter and gasket surface that kicked my butt once. Defective fuel filter threads.


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## texasag07 (Nov 11, 2014)

Ok all I’m back at this damn thing. All was fine for the last two months then started having the same issues.

Again I took the vst apart and it was again clogged about 30-40 percent with little black particles. 

So this time I replaced all the lines from the seperator and internally in the motor- now all lines in the boat have been replaced except for one of the factory molded lines that have lots of bends in it. I did pull this line and sprayed brake cleaner and then soaked it in gas for a while and ran some gas through it and do not see any black particles. The pieces of hose from the seperator to the first internal filter seemed suspect for sure very soft.

I also hooked up a small hand pump and pumped fuel through the low pressure pump to ensure no trash in it.

I then check all hose clamps and replaced the fuel/water seperator filter.

Then pumped the bulb with the engine side hose off of the primer bulb till fuel came out and reconnected it.

Took boat out and at first it would only run up to 3k rpms In gear. In neutral it will rev to redline. Fished for a bit then checked primer bulb as was able to get another pump or two till it got rock hard. After that engine would hit 43-4500. Ran it for about 30 mins with no improvement in rpm.

So I put it back on the trailer. At this point I’m thinking it’s air in the system. Took it home and idled it with muff’s on. Had wife pump the fuel bulb while I depressed the shradder valve on the top of the injector rail to try and let any air out. 

Hopefully test run it again tomorrow. 

Any other thoughts or suggestions?


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## texasag07 (Nov 11, 2014)

Test ran again last night after attempting to bleed it which I don't think should be necessary or helped and 4700-5000 rpm max any thoughts? @Boatbrains?

I'm going to try a find a fuel pressure gauge today and check running and idling fuel pressure other than cleaning the VST again in kinda out of thoughts.


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## Frank Ucci (Jan 20, 2019)

It's kind of a long shot at this point but... I had this same motor a few years back and found a hairline crack in the engine fuel filter housing. There is a single threaded rod which is cast into the plastic housing. This is secured to the mounting bracket with a nut. The crack develops around this rod and extends into the plastic top of the filter assembly. You can check this by having someone pump the primer bulb while you look for fuel to leak from any crack that might be in the housing. If that housing is cracked, it allows air to be drawn into fuel system at that point.


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## DONAGHUE (Nov 18, 2017)

I just saw this issue on a Vmax and it ended up being the high pressure fuel pump... got a rebuilt and good to go... 200ish


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## Finsleft258 (Oct 7, 2018)

texasag07 said:


> Ok all I’m back at this damn thing. All was fine for the last two months then started having the same issues.
> 
> Again I took the vst apart and it was again clogged about 30-40 percent with little black particles.
> 
> ...



If you did the fuel line and cleaned the VST, you still need to replace the high-pressure pump (they are not serviceable or cleanable) and clean the injectors again. Simply spraying out the injectors will not do. The screens in them need to be replaced.


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## texasag07 (Nov 11, 2014)

Finsleft258 said:


> If you did the fuel line and cleaned the VST, you still need to replace the high-pressure pump (they are not serviceable or cleanable) and clean the injectors again. Simply spraying out the injectors will not do. The screens in them need to be replaced.


The high pressure fuel pump was replaced approximately 6 months ago I did a quick fuel pressure check on it today on the trailer and its reading about 36-37 at idle and 43 when you turn the key off.

The injectors were checked by a shop with an injector test unit. They also clean injectors but said that cleaning was not necessary since all was good with them. Spray pattern looked good to the guy running it and me as well while I was watching. They also gave me new injector o rings and inspected the bushing/org that seals them in the intake as well.

I checked for cracks as frank said. There is a very tiny crack starting to form where frank mentioned. I pumped as hard as i could on the fuel bulb which was already hard and got nothing from that crack. I then opened the fuel shradder on top of the fuel rail while idling and shut of it. After doing this it let me pump it maybe one pump. I pressed on the bulb as hard as I could and no fuel came out.


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## DONAGHUE (Nov 18, 2017)

Neutral safety switch on the motor??? Seen this issue on a 200 Suzuki.... I'm reaching....


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## DONAGHUE (Nov 18, 2017)

It was a plunger type on the zuke... pain in the ass to get to


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## makin moves (Mar 20, 2010)

texasag07 said:


> The high pressure fuel pump was replaced approximately 6 months ago I did a quick fuel pressure check on it today on the trailer and its reading about 36-37 at idle and 43 when you turn the key off.
> 
> The injectors were checked by a shop with an injector test unit. They also clean injectors but said that cleaning was not necessary since all was good with them. Spray pattern looked good to the guy running it and me as well while I was watching. They also gave me new injector o rings and inspected the bushing/org that seals them in the intake as well.
> 
> I checked for cracks as frank said. There is a very tiny crack starting to form where frank mentioned. I pumped as hard as i could on the fuel bulb which was already hard and got nothing from that crack. I then opened the fuel shradder on top of the fuel rail while idling and shut of it. After doing this it let me pump it maybe one pump. I pressed on the bulb as hard as I could and no fuel came out.


 The crack might be expanding as it gets hot. However soft black particles you found sounds like bad fuel line. Probably the only one you didn't replace.


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## Finsleft258 (Oct 7, 2018)

texasag07 said:


> The high pressure fuel pump was replaced approximately 6 months ago I did a quick fuel pressure check on it today on the trailer and its reading about 36-37 at idle and 43 when you turn the key off.
> 
> The injectors were checked by a shop with an injector test unit. They also clean injectors but said that cleaning was not necessary since all was good with them. Spray pattern looked good to the guy running it and me as well while I was watching. They also gave me new injector o rings and inspected the bushing/org that seals them in the intake as well.
> 
> I checked for cracks as frank said. There is a very tiny crack starting to form where frank mentioned. I pumped as hard as i could on the fuel bulb which was already hard and got nothing from that crack. I then opened the fuel shradder on top of the fuel rail while idling and shut of it. After doing this it let me pump it maybe one pump. I pressed on the bulb as hard as I could and no fuel came out.


Did they measure volume output?


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## texasag07 (Nov 11, 2014)

Possibly on the expanding crack. I put a little epoxy on it last night to ensure no issues.

They did a volume test on the injectors.

Last night I also checked the tank check all and all was well. Also dumped the new water/fuel seperator and it looked fine.

I also opened up the low pressure diaphragm pump and all looks ok there.

I am going to pull the vst again and check for stuff in it, as well as replace the two lines I didn’t replace last time. I am going to use a small 12vlt autopump to pump the whole system once I reasemble. I will also have the injectors checkled one last time.


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