1996 Yamaha 115 saltwater series won’t run off idle

[SoundShark]

hey guys first and foremost thanks to everyone for all the help that’s been given to me so far.

So so after I rebuilt my carbs I cannot get the motor to run off idle.

I wass out last weekend when I got on the throttle to open her up and the engine began to bog. I was out with a buddy showing him the boat so I tried a few times to get it to clean up and it would not so I turned around and ran it slow just off idle 1800 rpm or so back to the dock.

The next night I checked the fuel strainer on the engine and also checked the compression 125-130 in all 4. And also checked for spark on all 4 coils. Everything checked out.

I then decided to pull both carbs and clean and rebuild both. I found a chunk of black material clogged into one of the main jets. I went thru all jets with wire and air as well as sonic cleaned the carbs and bowls and they all were clean and passing air and light. I then re gasketed both carbs and re installed.

I also installed a new fuel pump for good measure.

Fired the boat boat up and she ran PERFECT or so I thought. I unhooked and headed out of port.

I got out of the channel and dropped the throttle and baaaawwwwwwwww. Still bogging !

This is time it wouldn’t wind up at all and started vibrating at anything over 1/4 throttle.

i then tried full throttle and it just bogs and shakes and vibrates. I then turned around and went back to the dock at 1600 rpm.

i did notice when trimming the engine up it would rev a little then bog again.

Also so it will free rev in neautral ok. Just anything under a load it bogs and doesn’t want to run.

Could my primer ball be cutting fuel to the motor ?

I installed two new fuel filters about a month ago. One online right out of the tank and one spin on sierrra at stern right before fuel primer bulb.

Fuel seems to to be getting to the carbs as far as I can tell.

Im stumped on this.

is it possible I need to reset air fuel mixture screws ?

Please help !!

[panasonic]

How do the fuel lines look. You said you found black material in the carb...possibly black rubber from a fuel line coming apart inside?

Drain the float bowls and see if there is anymore of that black stuff in there again.

Did you try pumping the primer bulb when it was acting up?

When carbs went back on are all linkages are as they should be and the throttle is advancing the timing plate?

[SoundShark]

The exposed fuel lines all seem ok.
I will give them a closer look.
I squeezed the fuel ball only at idle and no surge or change in rpm.
The particulate that was in the main jet resembled a small plastic stone or something of that nature.
the little water separator screen had nothing in it (debris wise).
I have quite a bit of automotive engine experience and it almost resembles a vacuum leak.
I dis not check the ignition advance armature, where is this located ??
All linkages are hooked up and blades open fully at WOT, close fully at idle and partially open at full open in reverse.
The mechanical choke circuit blade opens and closes as it should.
i didn’t touch any of the air mixture screws when I cleaned and rebuilt the carbs. I left them in exactly how they came out.
Im super aggrevated, the boat fired up and purred like a kitten at idle, at anything above 1/3 throttle it just lugs and bogs, and shutters. No popping l,no coughing.

I just want to go fishing

[panasonic]

Please post exact model and Serial number data from the tag on the transom bracket. See if there is a Service manual to be had for all to see.

[SoundShark]

I have the service manuel.

Its a 1996 S115TXRU

[SoundShark]

I just remembered that I hooked up the choke solenoid and linkage after I rebuild both carburetors this was NOT hooked up prior to rebuilding the carbs could this be giving me my issue ?

Its #19 in the image:

[panasonic]

I just remembered that I hooked up the choke solenoid and linkage after I rebuild both carburetors this was NOT hooked up prior to rebuilding the carbs could this be giving me my issue ?

Its #19 in the image:

If the choke plates are not opening all the way after engine is running, this will cause running issues for sure, it will run rich. Leave intake cover off and make sure that the plates are all the way open after engine start. How were you starting the engine without the choke? If choke is sticking on...plugs will be black.

Timing plate is under the flywheel. It is connected to the throttle linkage and should be moving smoothly back and forth as you move the throttle from idle to wide open and vice versa. WITHOUT engine running, put it in gear, move throttle back and forth and watch the linkages on carbs and to timing plate. Reference chapter 3-2 in SM.

I am NOT saying your timing is off... just to check all linkages are moving freely as they should.

[SoundShark]

If the choke plates are not opening all the way after engine is running, this will cause running issues for sure, it will run rich. Leave intake cover off and make sure that the plates are all the way open after engine start. How were you starting the engine without the choke? If choke is sticking on...plugs will be black.

Timing plate is under the flywheel. It is connected to the throttle linkage and should be moving smoothly back and forth as you move the throttle from idle to wide open and vice versa. WITHOUT engine running, put it in gear, move throttle back and forth and watch the linkages on carbs and to timing plate. Reference chapter 3-2 in SM.

I am NOT saying your timing is off... just to check all linkages are moving freely as they should.

ok maybe I should have worded that better the mechanical choke was hooked up and working at all times.

I was reffering to the choke solenoid and solenoid pull rod. Neither the electrical connectors or the pull rod was hooked up when I took it apart.

What does this solenoid do exactly ?

Also it ran excellent with this stuff not hooked up prior to getting junk in the carb or whatever else may be causing this issue.

the issue now after cleaning the carbs is similar as before but different. The engine did not shake and shutter when it first occurred it just would bog and not go over 3000 RPM now it vibrates and shakes....

[TownsendsFJR1300]

ok maybe I should have worded that better the mechanical choke was hooked up and working at all times.

I was reffering to the choke solenoid and solenoid pull rod. Neither the electrical connectors or the pull rod was hooked up when I took it apart.

What does this solenoid do exactly ?

Also it ran excellent with this stuff not hooked up prior to getting junk in the carb or whatever else may be causing this issue.

the issue now after cleaning the carbs is similar as before but different. The engine did not shake and shutter when it first occurred it just would bog and not go over 3000 RPM now it vibrates and shakes....

The solenoid pulls the choke linkage (and choke) butterfly's closed WHEN ACTIVATED: https://www.boats.net/catalog/yamaha...xru/carburetor

As long as the choke shutters are OPEN once warm, the solenoid isn't your issue.


As noted, fuel lines can break down INTERNALLY with ethanol. It does sound as if your running out of fuel.

Have you tried draining the carbs (with just the drain screw), catch what comes out, looking for any debris.


When at the "problem RPM", have a helper squeeze the primer valve until hard and see if there's any change in performance. We're trying to see if the carbs are indeed getting fuel..


*Also, why did you initially rebuild the carburetors? What was your issue then?*

Depending on your answers, you may want to hook up a separate 6 gallon fuel tank and eliminate the built in tank (which may have a clogged screen unlet or not venting) and see if there's any difference in performance.. You may be getting just enough fuel for lower RPMs, but not enough flow when needed..

[SoundShark]

The solenoid pulls the choke linkage (and choke) butterfly's closed WHEN ACTIVATED: https://www.boats.net/catalog/yamaha...xru/carburetor

As long as the choke shutters are OPEN once warm, the solenoid isn't your issue.


As noted, fuel lines can break down INTERNALLY with ethanol. It does sound as if your running out of fuel.

Have you tried draining the carbs (with just the drain screw), catch what comes out, looking for any debris.


When at the "problem RPM", have a helper squeeze the primer valve until hard and see if there's any change in performance. We're trying to see if the carbs are indeed getting fuel..


*Also, why did you initially rebuild the carburetors? What was your issue then?*

Depending on your answers, you may want to hook up a separate 6 gallon fuel tank and eliminate the built in tank (which may have a clogged screen unlet or not venting) and see if there's any difference in performance.. You may be getting just enough fuel for lower RPMs, but not enough flow when needed..

Scott I had a similar performance problem so I decided to rebuild the carbs and found a chunk of debris clogging one of the main jets.

Ill check flow to carbs tomorrow night.

[SoundShark]

There was good fuel flow to the strainer before I removed the carbs to clean/rebuild. The carbs were initially cleaned in a parts washer to remove all oily and caked on grease. I then placed the seperated carbs and float bowls in our ultra sonic heated cleaner and let them cycle 3 times at 20 minutes per cycle @ 95 degrees.
After the three cycles I went thru all jets with an approprit size wire or paper clip to make sure all orifices were free and clear of any buidlup or debris. After this I then blew out all jets and fuel passages in both Nikki units with 120 PSI of shop air.
I then reistalled all new plugs and sealing washers and gasket directly from Yamaha overhaul kits.
I find it hard to believe that I "missed something" however I am human and I certainly make mistakes.
It seems as though this problem is fuel related however im wondering why the Original owner of the engine had the choke solenoid unhooked. Seems kind of strange to not use it.
Unless it was causing issues.
I will retrace fuel system up to the engine and see how its flowing up to fuel pump.
I will check to see if timining linkage is working properly.
I will also disconnect choke solenoid and see if it will run better without it.
Otherwise Im stumped.

[TownsendsFJR1300]

Sounds like you cleaned / went thru the carbs correctly and thoroughly.

I'd probably (as you noted), set the choke back up before any issues) and see what happens. Carbs may not be getting enough fuel when needed at higher RPMs.

Also, perhaps either hooking up a spark tester (if available) on each wire to the plug (when the issue arises) or a conductive timing light and verify you aren't loosing spark at the problem RPM's just to rule that out...

[99yam40]

I believe that would be an inductive timing light.

while the problem is happening ,monitoring the timing with a light and making sure all plugs are getting spark by moving the timing light from plug wire to plug wire will help rule out some things that could be causing your problem.
But then measuring the inputs and out puts of the CDI with proper test equipment might help as well.

if timing is advancing as it should and in spec and you have good spark while the motor is bogging down, it would have to deal with not enough fuel or too much.
With cowling and silencer off, spray some fuel mix into the different carb throats to see if that helps any.
there are off idle ports also in the carbs to help add fuel during the transition of throttle advance

did you do the link and sync procedure after reinstalling the carbs?
did you set the pilot screws to spec in manual ?

I once found a small piece of thin clear sheeting covering a jet in a carb I had just cleaned.I think it was some dried up fuel/gas mix that came loose from a fuel line or pump.
It is best to flush the lines some before filling up cleaned carbs

cleaning those small hoses on a motor is not an easy job

[SoundShark]

Ok so now I really feel stupid.

went to the boat today to try and start diagnosing the fuel system from the tank to the carbs.
i decided to start with the primer bowl squeeze test.
i ran the engine and got it up to
temp. My wife came with me to help out. We headed out of the channel and I goosed the throttle a couple times just to see if it bogged or fell on its face.
So here’s the interesting part. it started revving decent 2800 or so was achieved the. I backed off I was in a no wake zone.
I tried it one more time and I was successful as it revved to 3000 rpm I then backed it down.
at this point things were feeling,looking and feeling promising.
We exited the channel and past the no wake zone buoy.
I proceeded to drop the hammer slowly and the engine began gaining speed. It broke up a little then opened up to 5400 RPMs at plane.
I ran it at WOT 5400 rpms for about a half nautical mile then backed off.
I then let it idle for a few moments and went back up on plane and again settled out at 5400 at WOT. My wife asked if it was fixed and I had to think for a second and do one last test run.
My initial response to her was I don’t know...haha
I did my last run up to WOT and it ran great no bogging no issues.
Idle is still a little choppy but all in all it was ok.
Now another problem arose in my runs. The throttle was hanging on something and I was not able to get the engine into gear because of high revs and as soon as it hit neautral it revved to the limiter. I then proceeded to shut it down, pull the cowl and check the butterfly’s, linkages and throttle assemblies.
the armature on the port side of the engine was hanging up on the fuel lines it seemed.i pushed it away from the port side throttle linkage that runs to the back and made sure butterfly’s returned to full close.
I proceeded to re-fire the engine and put it in gear and began along my way back to port.

I don’t know why the boat ran fine on the second try however it is now running pretty well !
I also will need to purchase all new one fuel tubing from the fuel pump to the carbs.

Could this interferance have have been my issue all along ?

Also so any ideas on why it still idles a little ruff ??

Im now dumbfounded on why it is all the sudden running 90% better now after doing nothing at all ....

[99yam40]

you answer some of my questions and I will answer some of yours