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I have a serious issue with my 2003 Yamaha 115. The engine is an inline 4 cylinder with fuel injection. 106 hours.

Last fall I noticed it ran a bit "rough" at ~1900 rpm. It would disappear slightly below or above that RPM.
No other issues last year.

Prior to running it this year I changed the plugs, new fuel-water seperator and engine fuel filter. Running on internal tank full of fuel stabilized gas from last fall. On my season shakedown cruise 2 days ago, started fine, idled fine. Slowly warmed up, got on a plane, cruised at 32-3400 with out issue. After 10 minutes of running I stopped at an island dock for 5 minutes, engine idling.

After leaving the dock and slowly accelerating, it started to "bog down". I could not get on a plane and the engine sounded off, not smooth, like it was not running on all cylinders". In neutral, at 1300 rpm, you could hear it run rough. In gear, with full throttle the engine would not go above 2500. At one point giving it more throttle, it did smooth out for a few seconds, accelerate, then ran rough again. I limped home at low speed. I double checked spark plugs and wires are tight/good connection.

I was thinking of eliminating fuel as an issue by running it on a separate tank of clean gas prior to making the dreaded call to the dealer on Monday.

While I have a shop manual, my skill level on engines is basic. Can change plugs/fluids/fuses.

Any suggestions?

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the "not running on all cylinders", sounds like an ignition problem

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Phil,

New plugs can be bad. It has happened to me before.
Put the old plugs back in if you still have them and give that a try. This won't cost you anything to try out before spending time and money on the next step in the diagnosis.

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You may look in you gas tank ,the tank maybe oxion. Cut the fuel filter in half and look for small white parts in the paper, If so all you injectors will need to be changed and in the motor there are two small filters that will have to be upgraded>Bob Zollo

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Very interesting, I'd read about that causing issues before. Good luck and let us know what you find Phil.

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You can always try decarbing the outboard?

Seafoam

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Update -

Changed back to the old plugs. No difference.

Several of my boater buddies who work on their engines can't help since it is a late model fuel injected engine and not the straight forward 2 stroke carborated engines.

Will drain the fuel line/engine filter and hook up to a portable tank of fresh gas today. While I am very skeptical it is a fuel qualilty issue, it is the only thing left I can do with my limited skills.

:(

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Is this the first issue you've had with the engine since new? One other thing you could try to check and see if it's a vac leak would be to spray just a little fogger (using the thin red tube attachment) at the base of each injector while the engine is running, and listen for a change in idle, which would indicate a bad seal and air leak. Also, the new plugs that you removed, do they all look the same or does one look different from the rest, indicating a problem with one cylinder?

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This is the first issue with the motor. I run the engine with kid gloves, warm it up every time, no mashing to WOT etc.

I bought the boat in September 2005 and the motor had 32 hours on it. To date I have done the fluid changes and new plugs each year. Plugs bought at the local dealer.

The OLD plugs (still have them) all looked the same, a bit dirty but okay. The new plugs look fine.

Will look at the manual and engine and see if I am up for the fogger test. Got to say this engine is daunting compared to my old Yamaha 90 2-stroke.

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Before you call the dealer try doing the decarb on the engine.

Lets review: You had a slight problem last year before winter layup. you fogged the engine and then let it sit, all winter. You start it up, run ok, until you let it idle for awhile. Now all that carbon, is nice and gooey but not really going anywhere. Engine boggs down, runs rough. Switch back to old plugs, still runs rough, not a happy engine.
Most engine manufactures make some cleaning product to reduce carbon buildup.
Mercury - QuickClean
Yahama - Ring-Free
Generic - Seafoam

Sal's decarb technique

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Kamie -

I don't have carbs. It is fuel injected. I was on the water till October so didn't fog the cylinders. I ran it in December and February on muffs.

Maybe run some Seafoam/Ring Free from a separate tank?

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Certainly couldn't hurt to try, and if it was a injector issue, some sitting in there overnight may help. Have you had it running since the last outing when it bogged? Could you tell if it were normal or rough running on the muffs? Am wondering if it's an issue that happens when fully warmed up?

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I'm skeptical of the fuel quality (even w/ stabilizer).
mw

I'm also thinking possibly a small crack on a plug wire that can't be seen, and is grounding out as the motor climbs in rpm, cracked or faulty wire.

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Really sounds like restricted fuel. Have you checked your primer ball? There might be a problem with the check valve inside the bulb. Have you checked the vent on your gas tank? Some critter might have built a nest in the screen. Run the engine on a separated tank with a different gasline and primer bulb to the engine. See what happens.

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My 2004 90HP 4 stroke fuel injected ran great. I had an inline filter in the hose with a glass over screen filter (sold at Boaters World). I upgraded to a fixed screw on canister (size of engine oil filter) type. I had same problems you mentioned. I went back to the inline filter, no more problems. The engine would not draw enough gas thru the canister filter. It was to restrictive.

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My 2004 90HP 4 stroke fuel injected ran great. I had an inline filter in the hose with a glass over screen filter (sold at Boaters World). I upgraded to a fixed screw on canister (size of engine oil filter) type. I had same problems you mentioned. I went back to the inline filter, no more problems. The engine would not draw enough gas thru the canister filter. It was to restrictive.

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One other thought. When you took the fuel/water separator off did the gasket/o-ring come off and did the new gasket/o-ring seat? I don't think you have a major problem just a little rock in the road that is starving your engine for fuel.

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My money is on a fuel problem. I hope its something very simple.

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I am awaiting the verdict on this one since I am running twin 150 fourstrokes.

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Let me say, I really appreciate all of your advice and support with this.

Today I drained the fuel system and ran the engine on portable tank with clean gas. No joy. Have reviewed fittings, filter for any leaks.

I posted my symptoms on the Yamaha forum of I-Boats and Rodbolt (a Yamaha Master mechanic) suggests the cause is "..most likly gonna be a clogged filter on the high pressure pump or the injector screens are clogged"

I looked at the old water separator filter and bracket that I just replaced. I see lots of rust and crud on the inside of the bracket and ports. I think this may be the source of my problem.

In the shop she goes. Guess I know where my tax "rebate" check is going. Will post results.

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That's very frustrating after you've taken care of the motor, and not abused it, hope you get it back soon, I've had to use my tax return on my boat too, I've alway's thought it was money well spent !
mw

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Update -

Good news - They found time to look at the engine and found the problem. Could be ready next week. :)

Bad News - clogged injectors, VST filter, etc. Lots of $$$$. :(

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CBO,

At least you know the problem now. Did your old water separator filter and bracket cause the problem or your fuel tank? Did they recommend a different filter setup to prevent future problems?

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I think it was the rusting water separator filter bracket. While the outside looked fair, the inside was rusty. The tech did say the crud is brownish.

Prior to running this year I replaced the filter with the OEM Yamaha 10 micron mini. It is similar to the standard filters but the filter cartridge is a bit narrower and deeper. It is rated up to 120 hp. I also replaced 1/2 the fuel line. The other 1/2 will get done soon.

In addition to the fuel filter before the low pressure fuel pump, I learned there are two additional filters, one inline between the low pressure fuel pump and the VST and a second one in the VST itself. The VST is a bear to check since it is behind the fuel rail and the intake assembly. Accessing that one requires disassembly of the fuel rail, intake assembly and numerous hoses/connections.

When I pick up the boat (next Friday?), I will discuss his findings in depth with the mechanic to ensure I understand the precautions I need to take to prevent this happening again.

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I am back in business!

After talking to the mechanic at length, I learned she was only running on 2 cylinders, where the second fuel filter is along with the approach to removing the intake to get at the VST.

The big shocker learned is that the VST filter is an annual maintenance item (not in the service manual list). I was told that the inline 4 cylinder 115 is unique in placing the VST in a place that is not easily accessible. :o

Hope to get back on the water tomorrow (Sunday) despite a SCA. Still have to finish cleaning her up in preparation for the Piscat River gathering on June 1.

Just nice to have her back. I missed her! :D

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Glad you're back on the water today! Just curious if the injectors were able to be cleaned or did they need to be replaced? Sounds like that may have been the original filter in there?

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i asked yesterday, have you checked to see if it is overheating?
OP

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The injectors were sent out to be cleaned. Replacements are several hundred dollars EACH x 4.

I bought the boat with 32 hours on it. Now it has 105 ~ hours over 2 seasons so I considered the filter and VST membrane to be the original.

I would have changed them if they were listed in the operators manual as an annual item.

I plan on having the mech spend some time looking over the engine (in sub artic March) and walk me through what are the real maintenance items.

Cayman - There was no overheat. At the first sign of bogging down, limped home at 1100 rpms.

Despite an occasional fluctuation at idle, she is running great.

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Howdy. I have the same issue. The new ethanol fuels scour fuel sys. and wreaks havock. I have already cleaned my injectors and replaced the internal filters. I got them at Testmasters a local injector service and sales center. I used a rolled tip on a paddle drill bit to reach into the injector and hook the filter...and pull them out. Once out, I blasted the injector w/ walmart carb cleaner, attached a injector plug to a push button switch connected to 12v and "tapped" the switch while back blasting the injector w/ air then cleaner. 12 v continuous will burn the injector so you Tap or momentary contact operate them. When a fine cleaner mist is apparent from the supply side the injector is clean. I then pushed in the new filters. Gas psi from the engine is approx. 35psi so 80 or so will look great from an air nosel.
After injector cleaning the boat ran like a champ till I got "bogging " this past weekend.
My boat is a 19 Dusky w/ a fiberglass tank and I had run several tanks of 10% ethanol gas prior to epoxy painting the inside of the tank so I am sure the problems I have are from the ethanol eating my resin. I run a large primary filter. the secondary engine filter is being replaced, and I am about to return to the bench to clean the VST filter. I got the entire air intake/VST off in 1hr while watching the news and swatting skeeters. I know several Yam Mechanic and they all say this is something I could do.
I post what I find in the VST.
This is my fist time to this board...I do own a 13!
But I hope all are aware of the ethanol and the old fiberglass Montauk tanks.
The tank on the dusky is the large square forward console seat so cutting a large hole to get in and paint w/ epoxy was a breeze. Not so w/ the Montauk tanks..sorry.
cw

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Spent an hr cleaning the VST. It is basically a can w/ a float valve that regulates the immersion of an electric fuel pump. At the bottom of the pump is a rubber fitting housing the fuel pick up and screen. Mine was over half clogged. There are 400hrs on it. The plastic cover that guides fuel to the screen had a chunk of accumulated fiberglass resin that powdered under the pressure of my finger. the bottom of the can much like a carb bowl and was nasty w/ the same stuff.
I had it cleaned, re installed and running in an hr.

I love this motor!
I like my alcohol in my glass and not in my fiberglass tank/fuel system.
cw