Hunting & Fishing HEP! Yamaha 90 fuel problems? PROBLEM SOLVED!

[chevyrulz]

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UPDATE 8/16/12, PROBLEM SOLVED!!!!

new fuel pump ($50) fixed it



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hi, so i have a 2005 yamaha 90 2-stroke w/ about 70 hours on it. it was purchased new in box in 2009, and used on a 2001 Backcountry 151 proguide flats boat. the low hours are due to mostly local fishing & using the pole a lot.

the engine has run perfectly until last week when i think a fuel problem surfaced. it runs perfectly under 4000 RPM. when i am at 4500 RPM or higher, it will run for a while, maybe 30 seconds to 2 minutes, and then it will suddenly lose RPM sputtering as it either dies or drops to idle. it cranks right back up each time. when this occurs the fuel bulb is soft.

yesterday i replaced my fuel/water separator in hopes the issue would go away, but alas, it resurfaced. i got about 3 minutes of WOT (wide open throttle), running 5600 RPM until the issue came back.

My next step will be to replace the fuel bulb. the fuel bulb goes soft after the boat sits for a few days so maybe i'll get lucky & that's the culprit...

Next i may replace the fuel pump. local marine repair place tells me it could be in the fuel lines by the tank that there's a check valve which could go bad. that sounds like a pain since my tank isn't easily accessible.

i do not think it's electrical or carb related because it cranks & idles & runs perfectly under 4000 RPM. i can run for 2 days straight all over the place & never have a problem until i trim up & try to haul ass.

the only thing i've done recently which wasn't wise, is that i have gone airborne over waves & wakes a lot. that's why i changed the fuel/water separator because i suspected maybe i had knocked loose some sediment from the fuel tank.

are there things on the engine which i could clean or replace?

Any ideas appreciated, thank you

 

[Winged Pig]

Re: HEP! Yamaha 90 fuel problems?

Not sure about your particular engine, but I know of other Yamaha 2 strokes with those issues (specifically loss of power at high rpms) being rectified by replacing either or both, the VST filter or low pressure fuel pump(s). As I am not familiar with your engine I can't say for sure, but you might want to look there.

Sorry I couldn't help more.

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

^thank you for this info!

what does the "VST" stand for?
what does the VST filter typically look like?
where is the VST filter typically located?

haven't looked into the fuel pump yet so..

what does the low pressure fuel pump typically look like?
and where is it located?

trying to do as much repair/diagnosis as possibly myself before taking it in to the marine repair shop

 

[Winged Pig]

Re: HEP! Yamaha 90 fuel problems?

I believe it is the "vapor separation tank", and here are a few links that might help you out. I think the one is for a larger motor, so not sure it is exact. If I remember correctly the pumps are in the same area as this filter.

http://webpages.charter.net/stephens65/yamaha/8.html
http://forums.iboats.com/showthread.php?t=142168
http://www.thehulltruth.com/shipyard-isl-marine-engine-parts/222603-vst-filter-replacement.html#b

Here is a source for the pumps.
http://www.boats.net/parts/detail/yamaha/Y-692-24410-00-00.html

If you do replace the pump(s) I would stay away from Mallory pumps as I have heard of a few problems with them, but I have no first hand experience with them.

Hope that helps.

 

[Meat Hunter]

Re: HEP! Yamaha 90 fuel problems?

Replace bulb and add a double dose of Seafoam. Then when the problem clears up use the Seafoam in every tank. I have that exact motor and have never had one second of trouble. I use Seafoam full time. It may not be your particular issue but it is an inexpensive way to find out.

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Winged Pig</div><div class="ubbcode-body">I believe it is the "vapor separation tank", and here are a few links that might help you out. I think the one is for a larger motor, so not sure it is exact. If I remember correctly the pumps are in the same area as this filter.

http://webpages.charter.net/stephens65/yamaha/8.html
http://forums.iboats.com/showthread.php?t=142168
http://www.thehulltruth.com/shipyard-isl-marine-engine-parts/222603-vst-filter-replacement.html#b

Here is a source for the pumps.
http://www.boats.net/parts/detail/yamaha/Y-692-24410-00-00.html

If you do replace the pump(s) I would stay away from Mallory pumps as I have heard of a few problems with them, but I have no first hand experience with them.

Hope that helps. </div></div>
thank you very much!! now that i've read more about the VST, i don't honestly think it's the VST (not even sure if my 90hp has one?)

i replaced the fuel bulb but haven't been able to take a test drive yet. i discovered a dangerous trailer issue (rusted out bunk supports). they not only looked bad, but were structurally compromised (one whack with a hammer nearly broke it).... so the last couple days after work have been spent rebuilding my trailer. all new bunks, carpets, brackets, ubolts, repainted (cold galvanize spray paint). unbelievably, this cost me just $73 for everything not counting the crown staple gun i got for $25 from harbor freight (awesome tool for the bunk carpet by the way).

...my symptoms are unaffected by waves or shock or vibration. it doesn't seem to be starved for fuel when i hit a wave, but rather it seems starved for fuel after sustained high RPM. it's as if it keeps good fuel pressure at or below 3500-4000 RPM, but when i go above 4000 RPM, it eventually loses fuel pressure.

now i work a desk job, so i'm no expert mechanic, but from what i see, there's got to be a fuel pressure/volume problem. i almost did a little dance when i saw the new fuel pump is only $50!


as far as the check valve deal in the fuel line on the tank side, i found it. it's a threaded fitting on one end which connects to the fuel pickup hose & a hose barb on the other which connects to the fuel line leading toward the engine. this threaded/barb fitting has a check ball in side it to prevent fuel escape if boat sinks... apparently ethanol will gum these up & cause similar flow issues to what i'm experiencing. mechanic suggests i replace that fitting with a straight through, non check-ball, fitting. problem is it's a pain to get a wrench in there, & there's several different sizes of them....

after this fuel bulb test drive, if problem persists, then I will change the fuel tank check ball fitting. & if that doesn't work then the fuel pump. if that still doesn't work, i'm hiring a pro, lol

update to follow


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Meat Hunter</div><div class="ubbcode-body">Replace bulb and add a double dose of Seafoam. Then when the problem clears up use the Seafoam in every tank. I have that exact motor and have never had one second of trouble. I use Seafoam full time. It may not be your particular issue but it is an inexpensive way to find out. </div></div>seafoam can't hurt, might try that

 

[strick9]

Re: HEP! Yamaha 90 fuel problems?

Its about a fifteen minute job, staying organized, to remove the carbs and blow out the high speed jets, which is where I believe your problem most likely lies. The orifice of the high speed jets are tiny and any little debri that forms and breaks loose aft of the filter will clog the jet. You can google yamaha 90 carb rebuild and get a tutorial.

Seafoam may very well do the trick, I would say you have about a 50 percent chance of that working so I would try that first, run a couple of tanks through it with the recommended dosage and see if it improves, if not break down and clean the carbs brother. Pm me if you have any questions.

 

[Surffshr]

Re: HEP! Yamaha 90 fuel problems?

You said that you replaced the water separator filter, but did you check the little bowl on the motor? Any junk in there at all will screw you up and will point to needing to blow your carbs out. I'd check there before taking carbs apart. agree with sea foam treatments and doing the carb thing off that doesn't work. Did you replace fuel lines with the new motor? Need to have the ethanol resistant ones these days. Can be a source for crap in your fuel system. I'm using yamalube ring free plus in all tanks these days but sea foam is good stuff too.

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: STRICK9</div><div class="ubbcode-body">Its about a fifteen minute job, staying organized, to remove the carbs and blow out the high speed jets, which is where I believe your problem most likely lies. The orifice of the high speed jets are tiny and any little debri that forms and breaks loose aft of the filter will clog the jet. You can google yamaha 90 carb rebuild and get a tutorial.

Seafoam may very well do the trick, I would say you have about a 50 percent chance of that working so I would try that first, run a couple of tanks through it with the recommended dosage and see if it improves, if not break down and clean the carbs brother. Pm me if you have any questions. </div></div>
Thanks for the info & offer to help!! I've removed the dual carbs from a 25hp yamaha 2 stroke & cleaned them up. it should be basically the same thing +1 carb on my 90 yamaha w/ the 3 carb setup. hopefully, it will be a long time before i have to do that! lol, it's not hard, nor does it take long, but it's still no fun to clean carbs


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Surffshr</div><div class="ubbcode-body">You said that you replaced the water separator filter, but did you check the little bowl on the motor? Any junk in there at all will screw you up and will point to needing to blow your carbs out. I'd check there before taking carbs apart. agree with sea foam treatments and doing the carb thing off that doesn't work. Did you replace fuel lines with the new motor? Need to have the ethanol resistant ones these days. Can be a source for crap in your fuel system. I'm using yamalube ring free plus in all tanks these days but sea foam is good stuff too. </div></div>
thanks for the tips, i'm unsure of what type of fuel lines my boat is equipped with. it was repowered by a very good marine repair & sales company in 2009 so i'm sure they did it right. either way i only burn non-ethanol fuel unless i'm in a pinch. if i ever fill with 10% ethanol fuel, i always run it out ASAP & i would never store my boat for long term with that 10% ethanol in the system. i just bought this boat used about a month ago

 

[strick9]

Re: HEP! Yamaha 90 fuel problems?

liVE aND LuRN , Glad its running, I could tell you a thousand stories on how my hard headedness has turned a many a simple fix into a battle with the mysterious complex gremlin zombies.

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

ain't that the truth, luckily, i didn't fight this one too hard. i was just preparing for the worst by starting this thread

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

i swapped the primer bulb & <span style="text-decoration: line-through">now it runs like a champ all day @ 5800 RPM</span>. i held it wide open for 10 minutes without problem. i also upgraded the primer from the 1/4" OEM to the next size up, i think it was 5/16" if memory serves. i used a Johnson primer bulb because it was $10 cheaper than the Yamaha one.

i THOUGHT this fixed my problem, but the problem resurfaced on Sunday.

the boat had a full load, 4 people on board, whereas my prior test was me solo.

i think the load affected the fuel flow somehow. i had no problems running 4000 RPM, but it bogged out on me running 5600 RPM. i dropped down to 3500 & it stopped bogging out, then i kept on cruising @ 3800 all the way back to the dock (2 miles?) with no problems. when i leave the boat sitting, the fuel primer bulb goes soft. so i'm thinking the check ball in the anti-siphon valve is sticking & not fully opening or closing causing fuel to back flow into the tank resulting in a soft or empty primer bulb at rest & lack of flow @ high RPM. the straight through fitting should solve the high RPM issue, if my speculation is correct, but it will worsen the hard starting meaning i'd have to pump up the primer EVERY time i wanna crank my boat....so

now i'm going to change the anti-siphon valve on the fuel tank pickup fitting. i'm leery of swapping it for a straight through fitting as suggested by a very reputable marine mechanic. i realize it's ok per coast guard regs not to have this anti-siphon valve since i have an outboard & my fuel lines run ABOVE my fuel tank, but i still feel like i should replace mine rather than eliminate it. i'm going to see how it runs with the straight through fitting, & if that solves my problem, I'll buy a brand new brass anti-siphon valve & install it in place of the straight-through fitting.

if that doesn't fix this, i have to bite the bullet & replace my fuel pump, which thankfully is only like $50...update to follow

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

well i bit the bullet i guess, because yesterday i bought & installed a new fuel pump. it was $49 here locally. the damn thing took about 10 minutes to install, & 8 minutes of that was getting out tools & putting them back. 2 bolts hold it on, & 2 hoses connect to it, & it's right there on the side, super easy access. it was so easy, i am kicking myself for not starting with the fuel pump, lol. i will test out the boat this weekend & post an update

 

[chevyrulz]

Re: HEP! Yamaha 90 fuel problems?

fuel pump fixed it, ran about 2 miles wide open throttle with 2 people on board & no hiccups