Df115 trouble shooting rpm/ fuel issue

[Moonlighter]

Ok, have now tested the boat with the 2 non-return valves fitted in the fuel line.

As mentioned earlier, the primer bulb pumped up much quicker and stays firmer all day. So that is good.

But, the original problem persists! Damn! Did it 3 times yesterday on a trip on the Bay.

Does anyone know whether the neutral throttle switch on the engine works by cutting spark at 3000rpm, or by restricting fuel delivery?

My mechanic reckons that it isn't the neutral switch - his rationale is that this is because if it was, when the problem occurs i would notice the engine missing badly as the spark is cut by the e.c.u.

But, due to the lack of power and acceleration when the problem occurs, i don't think i have ever really got onto the plane and up past 3000rpm, which is where I understand that the neutral throttle cutout limit is. As soon as I realize that the problem i happening, I just throttle back, turn off, restart and away we go, good as new.

He wants to install a small electric fuel lift pump near the tank outlet to pressurize the fuel system and overcome what he thinks is a vapor lock issue.

Anyone tried that or heard of it making any difference?

What would you do?
(A) Fuel lift pump $100 plus fitting, cut into fuel lines etc
(B) neutral throttle switch replacement $60 plus fitting, plug in/plug out

Thoughts anyone?

[100 suzuki]

I have a DF100 i have the same problem, running good all day but when im heading back to the harbor and i throttle up it wont go over 3000 rpms , i also noticed that my fuel filter right before the mechanical fuel pump which i recently changed is full to the top only 1/3 way up. any ideas thanks.

[Moonlighter]

When you say "mechanical fuel pump", are you sure thats what you mean because there engines do not have one, it is an electronic fuel pump. Do you mean the primer bulb?

Re the fuel filter that is 1/3 full, when you installed it, did you fill it with fuel before you installed it? If not, remove it and fill it first, then re-install.

Sounds like it could be a similar problem to mine.

But check the primer bulb anyway, and fuel lines to make sure there is no obstruction, check all fuel filters too. particularly check the fuel tank breather to make sure it is not blocked. And check the fine filter inside the VST. Could be blocked with grunge from the old fuel.

If you do all that and still have the same issue, then all I can say is welcome to the club!

[kurttruk]

My problem ended up being the VST filter screen was full of junk. When the fuel started following it would clog up however when at idle or had low pressure it would work fine.

[100 suzuki]

I assumed that my fuel filter before my fuel pump wasn't full but I was looking at the water separation from fuel and the water, so I fixed that by draining the filter and gas tank and putting new fuel . I ran the boat several days later and still having the same problem no alarms but I tried stopping the boat putting it in neutral and shutting the motor down and restarting it , and it works runs like a champ again , then about hour later it does it again , so maybe ill try checking the that neutral switch on the motor side to see if that's the problem.

[100 suzuki]

What is a vst and where is located on the motor thanks

[aboard whatever]

Neutral Safety Switch

Grant,
The nuetral safety switch in the engine area is a common issue. I had to replace mine, but not for the reasons you guys are suggesting. Mine would not allow the motor to even turn over if it wasn't activated (button pushed in while the linkage was in nuetral). It's relatively inexpensive and easy to replace. I will follow this thread to see if that was your problem.
-Shawn

Shawn, Just joined this forum because of this very issue with my 2007 DF115. Luck and surprise that I stumbled on this posting. I do not have a Repair manual and was wondering if you know the part # of the Neutral Safety Switch and where exactly is it located on the motor? I had to rev up in hard reverse to get the boat off the trailer when launching, and when I got underway I couldn't go above 3000rpms without motor bogging down and acting as if it would quit. Just switched to lower rpms and got it back to the marina, general owners book suggested I should have brought back to neutral first. I am going to take the boat out and see if this happens again when the rains here stop, before I order another part. Thanks for any info. On a separate issue, does anyone know where on the parts list the throttle cables bracket might be listed? Somehow mine has disappeared and I have to place a cinch strap on to keep the cables inserted. Thanks, John

[landmine]

Loss of power after running at high throttle for about 30 minutes

I have a 2007 DF 115After a period of 4500 to 5000 rpm run the engine begins to drop away in rpm it's not a rev limiter as it will operate at above 3000 rpm if I bring the throttle back to match the revs. Sometimes it will drop away idle rough stall and on restart can be reloaded sometimes it goes perfect other times will not rev to full throttle.
I have drained fuel tank cleaned an d replaced fuel. All filters changed fuel lines changed and tank vent cleaned. Suggests on how to over come this problem welcome.

[artdf175]

In reading your question it sounds similar to this old 2012-2013 thread
Here are a couple of questions
The primer bulb what is the status of the primer bulb? Is it or does it remain full or is it deflated, so to speak?
Two other areas The filter in the VST high pressure pump
This has posed a problem on a number of different situations
Neutral switch on the starboard side of the engine where cables terminate from the helm
If this is not working correctly it is sending faulty signals to the ECU and can limit RPM
Art

[landmine]

Primer bulb remain inflated.
Where do I find the filter in theVSD pump?

[landmine]

Don't think it is being limited as would not run above 3000rpm?
Thanks Art

[Harper]

Primer bulb remain inflated.
Where do I find the filter in theVSD pump?

There's a small screen filter that fits over the intake at the bottom of the high pressure fuel pump in the VST.

[nelbur]

If you are having a problem where the engine runs fine and you shut down to drift awhile. When you start up again it bogs down as you start to climb onto plane, you might be having a vapor lock problem. This has been a problem for the Suzuki 4 strokes. They repaired under warranty engines using an electric fuel pump and a pressure regulator. Apparently the mechanical fuel pump does not pump gas vapor fast enough to keep the vapor separator filled with liquid, and it runs low causing the engine to bog. If this is your problem, when you start the engine after a drift, pump the bulb with the engine idling, to move the vapor out of the fuel system and get a hard bulb. If this solves the problem you have a vapor lock problem.

I have the problem on an '05 DF 140, but have done nothing to fix it as I normally troll, and it will run fine all day, until I drift. The fuel line runs between the intake manifold and the engine block where it could get heat soaked. I have thought I would re-route it down under the engine to keep it cooler. I have also noticed that Suzuki has redesigned the mechanical low pressure fuel pump to one with a V in the part number. I don't know if the V means it has addressed the vapor lock problem, but I would love to know.

[landmine]

Thanks nelbur for reply but it is not the problem I have with my 115. Problem occurs if I run 5000rpm or there abouts without moving throttle the revs start to fall away on a good day the engine continues to run but at reduced revs as long as you bring the thottle back to where it's comfortable. Others it dies away and stops. But when restarted its some times ok suspect the longer the time the better it is but have not proven that as I am always keen to get under way and continue to destination or head home in this case.

[humpinit]

This is an old thread but I will post my findings over the years in hopes of helping someone in the future.
I have an 06 df140. The problems that I have had are mostly with the 140 and down. The larger motors use a different fuel system.

It is crucial to keep water out of the fuel system and that is super difficult when using fuel that has ethanol in it. The ethanol sucks moisture out of the air. Running the boat every weekend and draining your water separator often should help with this. Or use non ethanol fuel (rec 90)'

This is why.
If your boat sits for too long the fuel in your vst will evaporate and any moisture in there will create a white chalky substance that will eventually clog up the vst filter. The vst is located behind the intake and isnt very hard to remove for a shade tree mechanic.

A bigger problem.
The fuel union on the bottom (maybe top) of the injector fuel rail is made of steel. This is the only piece in the fuel system that is made of steel that rusts. This little part is inches away, upstream from your injectors. It will make tiny little particles of rust that will clog one or all of your injectors. One or all slightly clogged injectors will create all of the symptoms that you are describing.

In my experience, I have been able to remove the injectors while on the water and tap the rust particles out of them and then re install for a temporary fix. You need to be careful not to drop any of the rubber grommets while doing this.

This drove me crazy for ever.

Good luck