Kubota L3710 runs for 20 minutes then won't run at speed or at all.

[Garman906]

Hello,

I'm hoping to get some insight to a fuel related problem that I have been fighting for about a week now. I was going to bush-hog my property and my tractor started right up after a long winter nap. I made several rounds around one field, approximately 20 minutes worth and the engine lost power and slowed way down. I limped it back to my garage and checked the fuel filter. It was dirty so I changed it and thought that everything would be ok. Started working again and approximately 20 minutes later, same thing. I have now replaced the fuel filter, lifter pump, all fuel lines and still have the same problem. I even removed the fuel tank and removed a stick and an old spout from a fuel can from it. I removed the fuel filter assembly and disassembled and cleaned it. I'm getting kind of desperate and thinking it may be something inside the injector pump. I don't really know exactly how the fuel flows through the injector pum or how to remove and replace it. It seems like if I remove a line or filter or just let it sit for a while it will start and run for another short spurt.

Any help would be greatly appreciated.

 

[ptsg]

Try this test. Run it for the 20 min or so it runs decent, then when it starts acting up, try taking the fuel cap off and keep running to see if it changes anything.

It's not uncommon for the vent on the cap to get plugged over time with dirt, dust, etc and causing similar issues.

 

[Garman906]

Thanks, I'll try that. Will update shortly.

 

[Garman906]

Try this test. Run it for the 20 min or so it runs decent, then when it starts acting up, try taking the fuel cap off and keep running to see if it changes anything.

It's not uncommon for the vent on the cap to get plugged over time with dirt, dust, etc and causing similar issues.

I tried that and got the same results.

 

[seville009]

How about your air filter? I always check that each spring before starting it due to critters nesting in it over the winter (and shredding the filter). Maybe it is clogged up.

 

[Garman906]

I've completely removed the air filters just for testing purposes and there was no change. I had just replaced both filters last year and they really aren't dirty.

 

[seville009]

When you say that the engine slows way down, is it still running smooth (like it would if you intentionally reduced the throttle), or is it sputtering/missing/rough?

 

[rbargeron]

Mouse or squirrel nest in the muffler? Something expanding with heat and plugging it up? Pet food? Acorns?

 

[Garman906]

When you say that the engine slows way down, is it still running smooth (like it would if you intentionally reduced the throttle), or is it sputtering/missing/rough?

It slows down smooth like it is running out of fuel., and has no power

 

[Garman906]

Mouse or squirrel nest in the muffler? Something expanding with heat and plugging it up? Pet food? Acorns?

Now that is something that I had not thought about. Not even sure how to check it, but I'll give it a whirl tomorrow. It does blow black smoke when I try to start it after it dies. Then after it sits a while it cranks right back up and runs great for another 15 - 20 minutes.

 

[Garman906]

One thing that I forgot to mention, because I didn't think it was important, but when it first did this weirdness, I pulled both side covers off to see if anything obvious was going on and found the rubber oil plug on the left side of the engine had blown out. The plug is old and age hardened and really doesn't fit that tight anymore, so I thought it probably was not related to the issue. I wrapped a thin rag around the portion that fits into the hole and tightened it up.

 

[seville009]

One thing that I forgot to mention, because I didn't think it was important, but when it first did this weirdness, I pulled both side covers off to see if anything obvious was going on and found the rubber oil plug on the left side of the engine had blown out. The plug is old and age hardened and really doesn't fit that tight anymore, so I thought it probably was not related to the issue. I wrapped a thin rag around the portion that fits into the hole and tightened it up.

you never know....sometimes the simplest thing can cause the problem.

if it were me, I'd put a proper plug in there before doing anything else.

Also...is your oil low?

 

[herm0016]

is the radiator getting hot? water pump pumping?

may be time for a compression test when cold, then right after its running rough/quits.

oil plug is evidence of crank case pressure, blow by.

seems to be heat related if it sits and comes back to life. test the injectors? I have heard of injectors that run well cold, but when they get hot do not.

sounds like you have covered the fuel system pretty well. have you checked the oil in the injector pump, if it is a separate thing to change like some, for evidence of wear.

 

[Garman906]

you never know....sometimes the simplest thing can cause the problem.

if it were me, I'd put a proper plug in there before doing anything else.

Also...is your oil low?

The oil was right up to the full mark on the dipstick.

 

[Garman906]

is the radiator getting hot? water pump pumping?

may be time for a compression test when cold, then right after its running rough/quits.

oil plug is evidence of crank case pressure, blow by.

seems to be heat related if it sits and comes back to life. test the injectors? I have heard of injectors that run well cold, but when they get hot do not.

sounds like you have covered the fuel system pretty well. have you checked the oil in the injector pump, if it is a separate thing to change like some, for evidence of wear.

The engine is not overheating at all. The temp gauge works (gets to the first white mark on the gauge) and I just cleaned all the gunk out of the radiator core last summer because the temp was getting too near the red on hot days.

How does this engine ventilate the crankcase? Does it have a pcv valve setup like the gasoline car engines used to?

Also, I think the cams and followers oil off the crankcase oiling system. I've never seen any reference to the injector pump cams having a separate oiling system.

 

[Leejohn]

Check and make sure you are getting good flow in and out at the filter. Could have a fuel line braking up inside.

 

[Garman906]

Check and make sure you are getting good flow in and out at the filter. Could have a fuel line braking up inside.

I have flow all the way to the injector pump. I replaced all the feed hoses and the lifter pump, took the filter assembly apart and cleaned it. I did find a chunk of dirt in the shutoff selector and thought for sure that was causing the problem, but it still happens.

 

[rbargeron]

Now that is something that I had not thought about. Not even sure how to check it, but I'll give it a whirl tomorrow. It does blow black smoke when I try to start it after it dies. Then after it sits a while it cranks right back up and runs great for another 15 - 20 minutes.

To check for a restriction, take off the left side panel and with a cold engine take out the four bolts 090 holding the muffler to the manifold flange. Clean the threads up so they turn easy and put two of them back in finger tight. Start it and run it till it starts dying, then turn it off. Loosen the two bolts a few turns, start it, and see if exhaust roars out the gap. Careful - everything will be HOT. Maybe use some sheet metal around it to avoid burning body paint.

Another idea is to take the muffler off and stand a piece of pipe in the hole instead and see if it runs better.

 

[Garman906]

To check for a restriction, take off the left side panel and with a cold engine take out the four bolts 090 holding the muffler to the manifold flange. Clean the threads up so they turn easy and put two of them back in finger tight. Start it and run it till it starts dying, then turn it off. Loosen the two bolts a few turns, start it, and see if exhaust roars out the gap. Careful - everything will be HOT. Maybe use some sheet metal around it to avoid burning body paint.

Another idea is to take the muffler off and stand a piece of pipe in the hole instead and see if it runs better.

View attachment 746245

Thanks, I'll try this today.

 

[JWR]

One thing that I forgot to mention, because I didn't think it was important, but when it first did this weirdness, I pulled both side covers off to see if anything obvious was going on and found the rubber oil plug on the left side of the engine had blown out. The plug is old and age hardened and really doesn't fit that tight anymore, so I thought it probably was not related to the issue. I wrapped a thin rag around the portion that fits into the hole and tightened it up.

What in heck is a "rubber oil plug?"