Yamaha 115 4 stroke sputter/stalling. Help!

[Markdelz76]

2000 Yamaha 115 4 stroke with 375 hours. Meticulously maintained and always ethanol free. I replaced VST, high pressure fuel pump and injectors 4 years ago (~150 hours, boat sat awhile it’s early years). Fuel filters and normal maintenance done yearly. I am having a weird issue that started the end of last season. It would sputter and pumping the bulb seemed to fix it temporarily. I just replaced the anti siphon valve and bulb and now pumping the bulb when the issue occurs does nothing. It did however seem to stay firmer, I do believe the valve was bad. I noticed that if I was ever below 2000 rpm, it would stall or sputter really bad. Any ideas?

UPDATE -
Replaced injectors and spark plugs. Put fuel pressure gauges on fuel rail and read 37 psi when running. Put fuel pressure gauge after low pressure fuel pump and read 10-11 psi when running. It is still stalling. Right before it stalls the gauges stay about the same, maybe go down a few psi. The idle air control valve clicks when I start and then turn off the motor. If the motor stalls, I do not hear the valve click. When it gets ready to stall, I hear it almost gasping for air, like an inhaling for air sound. Ughhhh

 

[seasick]

low pressure fuel pumps?

 

[Markdelz76]

low pressure fuel pumps?

I’ll check that out. Any way to test?

 

[seasick]

I’ll check that out. Any way to test?

Not easily. If it has never been replaced, it probably is time...
I see there is only one for your motor part number 6E5-24410-10-00

If you have access to a fuel pressure tester, the first step would be to test the pressure at the VST output. If the low pressure pump is bad, the VST will get starved for fuel and the high pressure out put will be low.
I don't have a manual handy to see what the pressure should be.
Also check that the inline gas filter (clear bowl) is not mucked up and that the bowl is seated correctly.
If there is a starvation issue, the problem is usually more pronounce at speed and load and yours isn't. Poor gas flow at low speeds that gets better at higher revs does point to the low pressure pump.

 

[Markdelz76]

Awesome. Thanks for your help! Have you had any luck with aftermarket pumps?

 

[seasick]

Awesome. Thanks for your help! Have you had any luck with aftermarket pumps?

I strongly recommend that you get a genuine Yamaha pump. There are some garbage pumps on the aftermarket world. The Yami pump is not that expensive, $50 maybe?

You may see that there are rebuild kits. Don't be tempted.

 

[Markdelz76]

I strongly recommend that you get a genuine Yamaha pump. There are some garbage pumps on the aftermarket world. The Yami pump is not that expensive, $50 maybe?

You may see that there are rebuild kits. Don't be tempted.

My pump is like $250 because I have a 4 stroke. Stinks haha

 

[seasick]

My bad.I did look up 2 stroke..
In this case, ignore my comments. I would definitely measure fuel pressure output at the VST first as well as checking filters and the like.
Are you able to squeeze the primer bulb (motor not running) until it gets firm?
When the motor acts up does the primer bulb collapse?
If you can see the level of gas in the clear filter bowl on the motor (cowling off), is the bowl complete full, empty, 3/4s full?

It is possible that the issue is not fuel but rather spark but that is a pure guess. To test that you need a spark tester gizmo. It is also possible to run the engine at a little speed in neutral and unplug the spark plug wires one at a time to see if the motor slows down. It should. Test all cylinders one at a time. Use a pliers with insulated handles and wear gloves when pulling the ignition wires. You can get easily zapped!

 

[Markdelz76]

My bad.I did look up 2 stroke..
In this case, ignore my comments. I would definitely measure fuel pressure output at the VST first as well as checking filters and the like.
Are you able to squeeze the primer bulb (motor not running) until it gets firm?
When the motor acts up does the primer bulb collapse?
If you can see the level of gas in the clear filter bowl on the motor (cowling off), is the bowl complete full, empty, 3/4s full?

It is possible that the issue is not fuel but rather spark but that is a pure guess. To test that you need a spark tester gizmo. It is also possible to run the engine at a little speed in neutral and unplug the spark plug wires one at a time to see if the motor slows down. It should. Test all cylinders one at a time. Use a pliers with insulated handles and wear gloves when pulling the ignition wires. You can get easily zapped!

Yep printer bulb is firm and did not help the issue when it was bogging down. I replaced plugs last year but will check them for sure. I did replace the coil packs 200 hours ago so they are new. The filters are all full. I start with plugs and then test pressure and confirm I am at 40psi at the rail and 10 psi after the low pressure pump.
Ugh these issues are annoying. I appreciate your help.

 

[seasick]

Good plan. One comment though; The clear bowl on the gas filter (motor mounted) should not be full. If it is, you may have an air leak somewhere. It is normally almost full.
Not seating the plastic bowl correctly is a common issue especial since the bowl rims tend to distort out of round.

The reference I made to the spark was to unplug each cylinder one at a time and confirm that the motor slows down or acts rough. At this point you do not need to pull plugs, just plug wires or use a spark tester ( cheap at Harbor freight)

 

[pikuptruk]

Do you have a picture of your anti siphon valve?

 

[Fishtales]

Have you been using fuel additives? Have you changed water separators? Condition of fuel? Maybe time for a double dose of ring free. May be water in gas.

 

[Markdelz76]

Have you been using fuel additives? Have you changed water separators? Condition of fuel? Maybe time for a double dose of ring free. May be water in gas.

No fuel additives. Ethanol free. Water separator changed and fuel filters. If water was in gas wouldn’t it run like crap all the time? Not just below 2k rpm?

 

[seasick]

I would check fuel pressure. Sputtering at lower revs could indicate insufficient fuel flow. That could be filters, fittings, VST screen or bad low pressure pump. When it sputters, try pumping the pr1mer bulb to see what happens. Is the bulb soft, or firm? Does the motor run a tad better when the primer is squeezed?
If you can replicate the sputtering at the dock, testing will be easier and only one person is needed. If it only happens at sea, you will need another set of hands to test safely.

 

[Markdelz76]

I would check fuel pressure. Sputtering at lower revs could indicate insufficient fuel flow. That could be filters, fittings, VST screen or bad low pressure pump. When it sputters, try pumping the pr1mer bulb to see what happens. Is the bulb soft, or firm? Does the motor run a tad better when the primer is squeezed?
If you can replicate the sputtering at the dock, testing will be easier and only one person is needed. If it only happens at sea, you will need another set of hands to test safely.

Yeah I tried pumping bulb when it was sputtering/before it died and nothing changed. Starting to wonder if it’s my idle air control valve. Going to the marina today to take a look

 

[DennisG01]

You said it runs fine above 2000 RPMs. I believe that eliminates the entire fuel supply system, correct?

I wouldn't think the IAC would affect anything above idle, right?

Gotta think about this one for a bit.

Wouldn't hurt to check fuel pressure, though. Also wouldn't hurt (and it's easy to do) to drain/check how much fuel is the VST immediately after a high RPM run and compare to when it was sputtering. These things will help eliminate/point to a supply issue. It also allows you to check fuel quality... although I'd be surprised if fuel quality ONLY affects low RPM running.

 

[chrisk]

2000 Yamaha 115 4 stroke with 375 hours. Meticulously maintained and always ethanol free. I replaced VST, high pressure fuel pump and injectors 4 years ago (~150 hours, boat sat awhile it’s early years). Fuel filters and normal maintenance done yearly. I am having a weird issue that started the end of last season. It would sputter and pumping the bulb seemed to fix it temporarily. I just replaced the anti siphon valve and bulb and now pumping the bulb when the issue occurs does nothing. It did however seem to stay firmer, I do believe the valve was bad. I noticed that if I was ever below 2000 rpm, it would stall or sputter really bad. Any ideas?

My son had a similar problem with his 115 Yamaha. Turned out to be spark plugs. Mechanic told him that the 115's need to have the plugs replaced annually. Did so and ran/runs great.

 

[Markdelz76]

You said it runs fine above 2000 RPMs. I believe that eliminates the entire fuel supply system, correct?

I wouldn't think the IAC would affect anything above idle, right?

Gotta think about this one for a bit.

Wouldn't hurt to check fuel pressure, though. Also wouldn't hurt (and it's easy to do) to drain/check how much fuel is the VST immediately after a high RPM run and compare to when it was sputtering. These things will help eliminate/point to a supply issue. It also allows you to check fuel quality... although I'd be surprised if fuel quality ONLY affects low RPM running.

Yep, above 2k and

You said it runs fine above 2000 RPMs. I believe that eliminates the entire fuel supply system, correct?

I wouldn't think the IAC would affect anything above idle, right?

Gotta think about this one for a bit.

Wouldn't hurt to check fuel pressure, though. Also wouldn't hurt (and it's easy to do) to drain/check how much fuel is the VST immediately after a high RPM run and compare to when it was sputtering. These things will help eliminate/point to a supply issue. It also allows you to check fuel quality... although I'd be surprised if fuel quality ONLY affects low RPM running.

yep above 2k all was ok. Once I pulled back, it sputtered and then stalled. I am definitely checking fuel pressure at fuel rail and after low pressure pump

 

[Markdelz76]

My son had a similar problem with his 115 Yamaha. Turned out to be spark plugs. Mechanic told him that the 115's need to have the plugs replaced annually. Did so and ran/runs great.

Yeah I changed them last year. Going to pull these today too

 

[seasick]

I wouldn't normally suspect the Idle Air Valve since it less important as the revs increase. Does the sputtering come on quickly as the revs go below 2000 and stop when revs over 2000? If the change is like an on/off event, I would look at what that motor does at 2000 revs. I don't know the answer but does the motor deactivate any cylinders at low revs?