Kubota BX sputters when hot and run at 3/4 throttle or more

[S.Wells]

Hi folks,

I have just about pulled out all three of my remaining hairs while trying to trouble shoot what seems to a be a fuel problem.

I have a 3 yr old Kubota BX 1850 with 420 hrs. All maintenance done on time per the manual.

Recently, it started acting up. Once the engine warmed up, it would sputter a bit and run rough, occasionally slowing down almost to idle, cough for a few more seconds, and then run back up to full throttle (or whatever the throttle was set at). It would then run fine for anywhere from 15 seconds to 5 minutes, and then do the same thing again... cough, slow, then back to the throttle setting.

I have replaced both fuel filters, replaced the fuel pump, replaced the fuel lines, changed the fuel itself, and now finally pulled, disassembled, and cleaned the individual components of each fuel injector. I've bled the system each time.

The **** thing still does the same thing once it's warm... it acts as though someone is closing the throttle to idle, and then eventually revs back up.

Anyone else have this problem? What have I missed? Do I have diesel gremlins? Maybe I fed the damed thing after midnight???

 

[charliechicken]

Hi folks,

I have just about pulled out all three of my remaining hairs while trying to trouble shoot what seems to a be a fuel problem.

I have a 3 yr old Kubota BX 1850 with 420 hrs. All maintenance done on time per the manual.

Recently, it started acting up. Once the engine warmed up, it would sputter a bit and run rough, occasionally slowing down almost to idle, cough for a few more seconds, and then run back up to full throttle (or whatever the throttle was set at). It would then run fine for anywhere from 15 seconds to 5 minutes, and then do the same thing again... cough, slow, then back to the throttle setting.

I have replaced both fuel filters, replaced the fuel pump, replaced the fuel lines, changed the fuel itself, and now finally pulled, disassembled, and cleaned the individual components of each fuel injector. I've bled the system each time.

The **** thing still does the same thing once it's warm... it acts as though someone is closing the throttle to idle, and then eventually revs back up.

Anyone else have this problem? What have I missed? Do I have diesel gremlins? Maybe I fed the damed thing after midnight???

Just today, I have a BX25 with the same attitude, just as it warms up, RPMs drop off and it sputters and shakes with no power than eventually the RPMs will come back up and it works fine for a min, 10 min or 30 seconds who knows, I have added fuel conditioner, and changed both filters, no change, maybe the fuel pump high pressure is the issue, I am Questioned as you are thanks

 

[North Idaho Wolfman]

Check/change the air filters as they can cause the same issues/symptoms as fuel.
Also check water levels and oil levels as overheating or low oil pressure can also cause some of the same issues.

 

[S.Wells]

Check/change the air filters as they can cause the same issues/symptoms as fuel.
Also check water levels and oil levels as overheating or low oil pressure can also cause some of the same issues.

Water and oil levels are fine. Just changed filters again even tho they only had about 20 hours on them. Really strange I can run it for hours under 2500 RPM but if I run the throttle higher it starts acting up after it gets warm. I am thinking to try changing the fuel solenoid. I am lost.

 

[hodge]

Have you checked and cleaned the fuel tank and pickup? You can have debris or bacteria buildup that will clog the pickup, restricting the amount of fuel supplied.

 

[S.Wells]

Have you checked and cleaned the fuel tank and pickup? You can have debris or bacteria buildup that will clog the pickup, restricting the amount of fuel supplied.

Yes all has been cleaned!! If it were some kind of debris you would think it would do it at all RPM's not just over 2500. It has to be some kind of mechanical or electrical problem.

 

[Profnohair]

See if the vent in the fuek cap is clear. (if the fuel is low enough in volume, crack the fuel cap and try it like that)

 

[hodge]

Yes all has been cleaned!! If it were some kind of debris you would think it would do it at all RPM's not just over 2500. It has to be some kind of mechanical or electrical problem.

Fuel demand is different at different RPM's- debris, or the suggested clogged vent cap, can cause starvation at higher fuel demands.
I doubt it is electrical- if it isn't a restriction, it almost has to be an injection pump issue, since you have eliminated everything else.

 

[scooby074]

How did you clean the tank? There is a bit of history with the BX tanks causing issues from dirt/rust.

Air filter is clean?

Id probably rig up a gauge on the inlet side of the injection pump and see if there is any fluctuation in pressure while in operation.

If thats ok and its still acting up, id probably pull the injectors and have them tested.

After that, really the only thing left is the injection pump, but Id put it being the injection pump pretty far down the list.

 

[freewheel3]

Hi folks,

I have just about pulled out all three of my remaining hairs while trying to trouble shoot what seems to a be a fuel problem.

I have a 3 yr old Kubota BX 1850 with 420 hrs. All maintenance done on time per the manual.

Recently, it started acting up. Once the engine warmed up, it would sputter a bit and run rough, occasionally slowing down almost to idle, cough for a few more seconds, and then run back up to full throttle (or whatever the throttle was set at). It would then run fine for anywhere from 15 seconds to 5 minutes, and then do the same thing again... cough, slow, then back to the throttle setting.

I have replaced both fuel filters, replaced the fuel pump, replaced the fuel lines, changed the fuel itself, and now finally pulled, disassembled, and cleaned the individual components of each fuel injector. I've bled the system each time.

The **** thing still does the same thing once it's warm... it acts as though someone is closing the throttle to idle, and then eventually revs back up.

Anyone else have this problem? What have I missed? Do I have diesel gremlins? Maybe I fed the damed thing after midnight???

To me, this sounds like you've got a fuel line collapsing. Maybe that's why it only happens when warm and the line is soft due to heat. I'd look real close at the fuel line, especially between the filters and the lift pump. It might be forming enough vacuum to collapse the line??? Does it do it at lower RPMs as well, or only at high RPMs? Can you run a temporary bypass line to see if the symptoms disappear?

 

[olthumpa]

Hi folks,

I have just about pulled out all three of my remaining hairs while trying to trouble shoot what seems to a be a fuel problem.

I have a 3 yr old Kubota BX 1850 with 420 hrs. All maintenance done on time per the manual.

Recently, it started acting up. Once the engine warmed up, it would sputter a bit and run rough, occasionally slowing down almost to idle, cough for a few more seconds, and then run back up to full throttle (or whatever the throttle was set at). It would then run fine for anywhere from 15 seconds to 5 minutes, and then do the same thing again... cough, slow, then back to the throttle setting.

I have replaced both fuel filters, replaced the fuel pump, replaced the fuel lines, changed the fuel itself, and now finally pulled, disassembled, and cleaned the individual components of each fuel injector. I've bled the system each time.

The **** thing still does the same thing once it's warm... it acts as though someone is closing the throttle to idle, and then eventually revs back up.

Anyone else have this problem? What have I missed? Do I have diesel gremlins? Maybe I fed the damed thing after midnight???

To me, this sounds like you've got a fuel line collapsing. Maybe that's why it only happens when warm and the line is soft due to heat. I'd look real close at the fuel line, especially between the filters and the lift pump. It might be forming enough vacuum to collapse the line??? Does it do it at lower RPMs as well, or only at high RPMs? Can you run a temporary bypass line to see if the symptoms disappear?

About 10 years ago I had a tractor that acted the same way, did not want to run at full throttle. Chased around similar to what you have done. Finely I took a new red refillable ketchup squeeze bottle filled it with fuel, attached a hose to it and to the fuel pump, started the tractor and it ran fine at full throttle. This prompted me to change ALL of my fuel lines and the tractor ran great. I then cut open all the old lines.
My problem turned out to be a fuel line that had separated and the inside was collapsing under the suction at full throttle but the out side of the line looked fine.

Just one lesson I have learned.

PS. the "old" line was less than one year old so it was the last thing I thought it would be. Defective line.

 

[S.Wells]

Just wanted to let you guys know I did find the problem. There was a bug restricting fuel flow in the 90 degree fitting that comes out of the bottom of the tank that the main fuel line connects to. Amazing how something so simple can be so hard to figure out. I had drained the tank several times, changed fuel filters twice. Cleaned inside of tank best I could and really didn't find any type of debris. One bug maybe a June bug that had been sucked into that fitting and fit perfectly. Now I had to remove the tank to pull that fitting which wasn't easy but well worth it.

 

[ipz2222]

And you just have to ask,, How did a bug get in the tank????

 

[olthumpa]

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." - Arthur Conan Doyle

Glad you solved the puzzle.

 

[skeets]

I thought Spock said that

 

[S.Wells]

And you just have to ask,, How did a bug get in the tank????

Exactly! One little bug causing so much headache!!

 

[wfd2]

Exactly! One little bug causing so much headache!!

I'm having the exact same problem with my BX23 and I am running low on hairs, too.

When I changed the first fuel filter, I noted that full pressure fuel was coming out of the line. So I assumed no restriction. But I wonder why your's would heat up then start sputtering? I dread taking the tank down to inspect but looks like I will have too. How did you find the bug? Finally just fall out upon second inspection?

 

[netxtown]

Just wanted to let you guys know I did find the problem. There was a bug restricting fuel flow.

Ok...so it kind of has a 'funny' ending - but this is happening all to often. I had the problem a couple years back on my 1850....and yep, smack in that 90° fitting was a beetle of some sort. I was still under warranty - and i was sure it was some super-technical issue....so about $500 later the dealer showed me the bug. Fully pickled -still not edible.

Since then, I have been incredibly cautious when the cap is off....and ALWAYS put a super-fine weave household strainer in place any time the tank is open for filling.

And now...it's b-a-a-a-c-k!! Mine idles fine...but sputters under any load - other than a heavy load on a steep incline.
Pulling the filter is a whole lot easier!

I also have only 3 hairs left - and i haven't pulled the tank before. Does the whole rear plastic body have to come off? If I have to do it, I will. And I will be inclined to implement something to make sure I don't have to do it again. Others have noted the rust/sediment problem....so a pitcock of some sort.....