DF140 Surging Issue

[MarshMarlowe]

Hey everyone, new to the forum, and wouldn't you know it, I joined because I'm having an issue with my Outboard - 2008 Suzuki DF140 / 180 hours

I did some searching here on the forum for issues similar to mine, and it seems most everyone is having a bogging issue throughout all RPM ranges or their engines are bogging around 3000 RPM's which could indicate a faulty neutral safety switch. My issue is a bit different.

A few weekends ago was when I noticed it first. I would run the boat WOT (5500-5700RPMs), and very occasionally the motor would act like it caught air and briefly drop about 200RPM's, then hop back up to WOT. It would run fine for 30 seconds or so, then drop, then run fine again. So I changed the spark plugs and the fuel/water separator, ran it again recently. At first it ran fine for 30 seconds, then slowly dropped 500-600RPMs. I actually took a video of this happening- here it is. At 1:00 minute into the video you will see the RPM's drop: Suzuki DF140 Surge Issue 1 - YouTube

When I throttle back from WOT, the problem disappears. Seems like I can run all the way up to 5000RPM's without any issue.

Then, on the way back in, I tried to run WOT again, and the surging became dramatic - the engine would suddenly drop from 5500RPM's all the way down to 1500RPM's, then jump back to WOT, and repeat in that fashion. I took a video of this happening too, you can see it at 00:35 into the video - here it is: Suzuki DF140 Surge Issue 2 - YouTube

I've set up a remote tank with fresh fuel and a fresh primer bulb, and I intend to run the boat tomorrow to see if anything changes. People have told me to check the intake screen at the VST (I searched for this too). The VST appears to be behind the intake manifold, and will likely required the intake manifold to be removed to gain access. Has anyone here done this before? It looks a little involved to me. I have not changed the low pressure filter or the high pressure filter because I have not accumulated enough hours on the engine to warrant changing them yet. Should I?

Thanks for any help!

[MarshMarlowe]

So, I ran the boat on the remote tank tonight with a new primer bulb... same symptoms.

My plan is to replace all the fuel lines, change the low pressure and the high pressure filter, drain the fuel rail and fuel cooler, replace the filter on the VST intake, and clean out the VST, then try running the engine again.

Looks like most of the fuel lines snake back behind the intake manifold, and the VST is more easily accessible with the intake manifold removed. Does the intake manifold have a gasket that will need to be replaced for reinstallation?

Thanks

[BeachGuy]

I am experiencing the same problem as you. I have cleaned the fuel tank, installed new fuel lines and new external fuel filter. Still have the same problem as you.

Have you been able to find a solution?

BeachGuy

[MarshMarlowe]

*

I haven’t quite sorted it out for sure yet.* I’m in the process of swapping this motor over to another boat, so I haven’t been able to test out a fix.* I’ve been talking to a dealer about it, and he suggested I try draining the VST tank (very easy) and closely examining the fuel to see if it was dirty or separated.* I did this, and the VST tank was clean.* I then disconnect the fuel line that runs from the HP fuel filter to the fuel cooler, hit the key and pumped out some fuel from there to see if the HP fuel filter was clogged or dirty.* No issue there.

*

One thing that’s been weird about my motor – I have to prime the fuel bulb almost every time before I start it.* Other people who own this outboard say they never have to prime it at all.* I told the dealer this, and he said I might have an issue on the low pressure side, and suggested that when the outboard begins to surge, try squeezing the bulb to see if it goes away.* I did this, and it went away.* So I suspect the low pressure fuel pump is failing – it’s pumping enough fuel into the VST tank to keep the engine running at 5K or less RPM’s, but not enough to keep up with the demand at WOT.* I ordered a new LP fuel pump, but I haven’t had a chance to test it out yet.

*

Thanks for the reply – I forgot I even posted this over here.* I’ll update here once I find a fix.

*

[BeachGuy]

Update

For what its worth, you may have already tired this.

After testing all the suggestions on this tread and others that I researched here is my final outcome.

Drain all the fuel for a aluminum fuel tank that is 26 years old.

Removed the fuel tank and then steam clean the outside (hoping to loosen what was inside) then doing the best I could steam cleaned the inside of the tank.

I found that the small ball in the pick up tube (screwed into the tank) that acts as a one way fluid valve was no longer seated by the spring. Remove spring and ball and did without it.

Replaced both the tank vent and the fuel filler hoses.

Replaced the external fuel filter with new and then installed 15 gallons of new fuel.

Ran the boat for 5 hours on Memorial Day and had to drain the fuel filter three times. After that the motor ran really well.

I believe that my problem was from 1. a bad vent line and the tank not venting as designed. 2. the crude in the fuel tank. 3 the nonfunctional one way ball valve in the pick tube.

Prior to my problems, the fuel filter never picked up the crude in the tank, and the primer bulb would all way collapse when under heavy power.

Now lest hope this solves my problems.

[noelm007]

You mentioned you hadn't done enough engine hours to need to replace the filters!! dirty fuel will block a filter in minutes, it has nothing to do with engine hours' filters are the first thng to replace if you are having fuel issues.

[timkadams]

What was the fix? I'm having the same issue; I replaced all fuel lines, pickup valve, anti-siphon valve, pump ball and nothing works. The last time I ran my boat it went to WOT (5500 rpm) for a few minutes and surged back down to 500-1000 rpms. I can use the pump ball to force fuel into VST only to give it fuel to return back to the boat ramp. Last year this started and I replaced all the filters, fuel lines to and from the VST and LP fuel pump, presure regulator and LP fuel pump. The problem ended for a few weekend of boating and returned this summer, even worse. I'm thinking about changing the spark plugs and take the VST apart to see if it has junk in it. My last resort is to replace the VST unit. Please provide any comments.

[MarshMarlowe]

I believe I have found the fix. I'm a little embarrassed to admit what was causing the surging issue. A Suzuki Dealer pointed this out, and it seemed too simple to be the problem... but it was.

On my old boat, I had my fuel line rigged with the primer bulb dangling underneath the engine. This was causing a right angle kink in the soft gray fuel line, and over time, the kink got worse causing enough of a blockage to create my surging issue. See the picture:




Since I had the motor rigged on my new Key West, the guys at the plant rigged it up right and the surging problem is gone. The issue with me needing to prime the bulb before I start the engine is gone now too. So, for anyone having a similar issue that doesn't seem to be caused by the VST screen, I'd say a fuel blockage exists somewhere. I did change the Low Pressure filter before it was re-rigged, but I checked all the fuel in the engine and the filters, and it was all clean, so I don't believe the filter caused this, but that doesn't mean it couldn't have if it were partially blocked.

Thanks to everyone who offered their input. I hope this post helps someone else in the future

[JonCase]

I know that this is an old thread but did other who had the same problem manage to fix the issue? My 2010 DF140 is currently surging like this dropping from 4500rpm down to 1000 and then back up.

I will check that the fuel lines are not kinked but was there any other solutions out there?

[Seaark1]

I'm having the same issue. I replaced everything fuel related to the motor last year and 2 weeks ago bam same thing. Half throttle it runs like a new motor, anything over that it surges.