YM 3110 Surging issue

[fltengineer]

Got a new issue that has cropped up on me and wanted some advise before I tear into it.

While brush hogging my pasture, after approx an hour the engine will begin surging by about 100-250 rpm, if I do not touch anything the surging will progressively get worse and get to 500 rpm surges. The engine will also begin losing power like its being bogged down while the surging happens and get to where it doesn't wont to run.

If I stop and idle down a little but for a few minutes, the engine will again run fine for another 5mins or so before starting with the surging again. If I disengage the PTO and pull back to a cool down idle the engine will not maintain an idle and will shut off.

If I let the tractor sit for about 30mins turned off and come back to it, it will again run fine for about an hour and then start to repeat the same issue.

Temps and oil pressure are all normal, fuel filter is clean and fairly new (maybe 10 hours on it), fresh tank of fuel, air filter has about 25 hours on but "looks" fairly good.

So some things I read on other tractor makes is debris in the fuel intake line choking out the engine or possible injector issues.

Any ideas on where to start or what the possible issue could be. Im hoping its as simple as flushing lines and the tank.

Thanks for any help provided on this.
Jason

 

[YanmarFever]

Jason,
I think you're on the right track with cleaning out the fuel tank and replacing the fuel lines.

 

[6thgpSF]

check your fuel cap for venting...russ

 

[Ginormous]

check your fuel cap for venting...russ

This is where I would start.

 

[fltengineer]

So....first thing this morning.....checked water level, and oil levels (just in case).
Started up the tractor and broke open the lines at the injectors, then the manifold. Fuel was flowing fine.

Started on the field again and sure enough, about an hour into it, it started surging again.

How would I check for venting at the fuel cap?

Dreading dumping fuel from the tank since its full, but that will be the mornings project I guess.

***Side note***
Not sure if it was my mind playing tricks on me but I thought when I had the tractor at full run (2500'ish RPM) I was hearing what sounded like a very very soft back fire type sound, almost like a burping sound, but so soft you had to really pay attention to hear it. I only noticed it because it was a new noise from the engine.

 

[winston1]

Not sure how the 3110 cap vents. Some models have a strainer and if that strainer is not in place it will not vent. Just try loosening it for a test. How about decreasing your rpms down to around 2200 and just see if it makes any difference? Yanmar Tractor Parts: Fuel Tank Screen

 

[Roonabeck]

fuel filter is clean and fairly new (maybe 10 hours on it)

Sounds like this started pretty soon after the new fuel filter was installed? Perhaps the fuel bowl didn't quite seal properly and there's a tiny leak that opens up when the engine warms up and lets air bubbles into the fuel line?

 

[Car Doc]

The cap on mine isn't vented I dont know the reason it isn't but but I leave mine just loose enough so it will vent but not work itself off.

One day shortly after I bought it on a hot day I happened to look at the tractor and noticed my fuel tank was missing!

Closer inspection revealed the plastic tank had sucked down into itself so far the cap and top of tank was 6-8" inside the cowling.

I released the vacuum and its been fine since as long as I leave the cap just right.

 

[6thgpSF]

another thought,did you replace the O ring when you changed fuel filter?...russ

 

[fltengineer]

Thanks all for the help with the brain storming.

Think I got it fixed today.....

Pulled the filter bowl and reseated it, went from the tank down and re-drained all the lines to the injectors. Headed to the pasture and ran for just over an hour with no issues, so I'm crossing my fingers that it was just the O-ring on the filter bowl not being seated good.

Oh and for the side note about the new odd noise.....turns out one of the packings on the exhaust manifold had failed, and what I was hearing was the blow by where it failed. So I pulled the manifold and replaced the packings. No more noise or blow by there

Nice how something small and annoying helps find something that could have been worse.