How does the Kubota BX fuel tank vent?

[Jon Baughman]

I am getting a vacuum in the tank line to the fuel pump. This causes the fuel flow to stop until I pull the line and release the vacuum, then the tractor runs until the vacuum develops again.

I am wondering if there is a blocked vent. I used an air compressor to blow air through the fuel return line with that tank filler cap on. The tank vented that air out of the cap, but I don't know how air is allowed into the tank during normal operation?

I am certain that there is no clogged lines, filters, or tank outlets. Fuel will freely flow all the way to the injectors when the vacuum is released. I have allowed the fuel to flow out of the tank line many times with no evidence that there is a clog there.

Any ideas?

 

[armylifer]

I don't know exactly how the fuel tank is vented but I think I once saw a comment that it is vented through the tank cap. Try running your tractor with the fuel tank cap a little loose and see if that helps your tank vent. If it does not develop a vacuum then you have found your problem. I cannot offer a solution to fix it other than maybe getting a new tank cap. There may be some sort of a rubber vent valve in the cap that is clogged. As I said, I don't really know for sure but maybe try blowing air through the cap and make sure that it is thoroughly clean.

 

[Trimley]

I'm pretty sure the cap of the tank vents both ways. If not, there could be (guessing) a vent coming off the tank with a down tube?

Here's a thread on OTT

 

[Henro]

I'm pretty sure the cap of the tank vents both ways. If not, there could be a vent coming off the tank with a down tube.

I have come to believe the BXs vent the tank through the filler cap. Been a number of threads here over the years about this, at least one I remember actually had pictures or drawings explaining how.

If the OP takes a good look at the tank cap he may see how it works and why his isn't.

He might also run the tractor with the cap loose and see if the problem occurs then or goes away. Just to ensure there is not something else going on somewhere...

Edit: Also look at the filler itself. Are there groves cut in the threads? I faintly may remember this is part of the venting system...but I don't put much faith in my memory these days...

 

[Jon Baughman]

My BX is only 3 years old and I only use it to mow my lawn. In the past I do recall having a noticable amount of gas escape the fuel cap when I unscrewed it for refuling.

My thought is that as the pump removes fuel from the tank, then the one-way intake valve would allow air to come in to replace the volume that was removed by the fuel being pumped out and creating a slight positive pressure inside the tank.

I don't notice and air escaping when I remove the cap anymore. I didn't know if that was a clue. I have tried to open the fuel cap in an attempt to relieve the vacuum in the line, but that has not worked.

However, when I pull the line off of the pump the vacuum is instantly relieved and fuel immediately gushes out of the inbound line to the lift pump.

I am a novice, but it seems to me that this fuel problem has something to do with venting in the tank, or maybe the fuel line is being pinched off by way of how it is being routed to the pump from the tank?

I do know for sure that the fuel line is oval in shape (not round), when I go to remove it from the inbound side of the lift pump. There is a rush of air into the line when I remove it, and fuel immediately flows out with no evidence of obstrution.

Also, important to note that I have completely removed the primary filter and bridged the line with a 2 sided barbed fitting, so that fuel filter is gone out of the system and is not a factor.

 

[armylifer]

My BX is only 3 years old and I only use it to mow my lawn. In the past I do recall having a noticable amount of gas escape the fuel cap when I unscrewed it for refuling.

My thought is that as the pump removes fuel from the tank, then the one-way intake valve would allow air to come in to replace the volume that was removed by the fuel being pumped out and creating a slight positive pressure inside the tank.

I don't notice and air escaping when I remove the cap anymore. I didn't know if that was a clue. I have tried to open the fuel cap in an attempt to relieve the vacuum in the line, but that has not worked.

However, when I pull the line off of the pump the vacuum is instantly relieved and fuel immediately gushes out of the inbound line to the lift pump.

I am a novice, but it seems to me that this fuel problem has something to do with venting in the tank, or maybe the fuel line is being pinched off by way of how it is being routed to the pump from the tank?

I do know for sure that the fuel line is oval in shape (not round), when I go to remove it from the inbound side of the lift pump. There is a rush of air into the line when I remove it, and fuel immediately flows out with no evidence of obstrution.

Also, important to note that I have completely removed the primary filter and bridged the line with a 2 sided barbed fitting, so that fuel filter is gone out of the system and is not a factor.

Two things to note here. One the fuel line should not be oval it should be round. The fact that it is oval indicates that it is being pinched someplace in the line. Two there are two fuel filters on your tractor. One is located by the engine compartment and the other is located under the tractor generally in the area of the seat.

 

[Jon Baughman]

Update;

My BX2380 ran for several hours with no problem (mowing the lawn). We'll see if this continues to be the case.

These are the steps that I have taken:

I have removed the primary fuel filter and connected the fuel lines with a barbed fitting.

I blew compressed air through the return line off of the engine.

I removed the fuel cap and observed that the vent holes were filthy. I used a small flat blade and dug out the vents and then I blew compressed air in each one. I also tapped the cap onto a hard surface trying to knock out more debris.

I then blew compressed air through the 2 vents on the inside of the fuel cap.

I filled the tank with new fuel from the local gas station.

No problems so far.

I'll continue to run it and see what happens.

I love my tractor and it has really improved things for me around my property, but this issue has been very aggravating for me. I know from my research that this seems to be a common problem for BX owners.

I realize that there are different issues that affect each case but there also seems to be some similarity between the cases.

I feel strongly that Kubota must evaluate this and issue a recall or at a minimum acknowledge the problem and offer solutions to owners through a bulletin. It is unacceptable to have a new tractor fail like this with such light use.

 

[armylifer]

Update;

My BX2380 ran for several hours with no problem (mowing the lawn). We'll see if this continues to be the case.

These are the steps that I have taken:

I have removed the primary fuel filter and connected the fuel lines with a barbed fitting.

I blew compressed air through the return line off of the engine.

I removed the fuel cap and observed that the vent holes were filthy. I used a small flat blade and dug out the vents and then I blew compressed air in each one. I also tapped the cap onto a hard surface trying to knock out more debris.

I then blew compressed air through the 2 vents on the inside of the fuel cap.

I filled the tank with new fuel from the local gas station.

No problems so far.

I'll continue to run it and see what happens.

I love my tractor and it has really improved things for me around my property, but this issue has been very aggravating for me. I know from my research that this seems to be a common problem for BX owners.

I realize that there are different issues that affect each case but there also seems to be some similarity between the cases.

I feel strongly that Kubota must evaluate this and issue a recall or at a minimum acknowledge the problem and offer solutions to owners through a bulletin. It is unacceptable to have a new tractor fail like this with such light use.

What you have done is performed normal maintenance. The things that you did are what every tractor owner has to do to keep their machines working.

Think about how your tractor is subjected to dirt and dust every time you are using it. That is what is causing the maintenance issues, not a poor design.

 

[Trimley]

I've been to a Blow Mold factory and watched the process of making water tanks. When the plastic is drilled to install something, there is flash (shavings) inside that need removed.

I've read of many problems coming from BX owners who've completely removed the fuel tanks to find shavings and plastic remnants. That's enough validation for me to feel the quality control regarding the issue is nil to none.

I've also seen images of the low quality fuel sending units that are used, covered in rust. Rust draws moisture and creates a breeding ground of more problems.

 

[GreensvilleJay]

gee I'm impressed you got 3 YEARS worth of grass cutting (and whatever else) before the fuel cap got plugged up ! I've got 1130+ hrs on my BX23S (same tank,etc) and never had it plugged up though I don't cut grass. I have gone through a dozen air filters due to the dusty conditions I've had to use my lil TLB. EVERY fillup( 10L) I inspect the cap and usually hose it down every month or so.
As for the tank and sensor, those can easily be dealt with, Kubota could pay $$$ for every tank to be 100% inspected and use Stainless steel in the fuel sensor or better yet, use an electronic level sensor. Both though will add $100-$300 to every tractor.....so are YOU willing to pay that ?

 

[MapleLeafFarmer]

I am certain that there is no clogged lines, filters, or tank outlets. Fuel will freely flow all the way to the injectors when the vacuum is released. I have allowed the fuel to flow out of the tank line many times with no evidence that there is a clog there.

Any ideas?

I notice you didn't mention anything about your piping post injectors?
Suggest maybe you check your fuel overflow line just in case pinched or plugged.
i have never seen one plugged but I have seen pinched lines from shade-tree guys who didn't take care when working on tanks, etc...

This pic from a BX WSM.

 

[Trimley]

As for the tank and sensor, those can easily be dealt with, Kubota could pay $$$ for every tank to be 100% inspected and use Stainless steel in the fuel sensor or better yet, use an electronic level sensor. Both though will add $100-$300 to every tractor.....so are YOU willing to pay that ?

An ounce of prevention is worth a pound of cure, considering the issue I AM SURE they are aware of, and it should be addressed and remedied.

 

[GreensvilleJay]

Regular preventive maintenance by the owner would deal with the fuel filler cap. It's probably in the owner's manual that no one ever fully reads....
Guess I should finally read my 5 year old owner's manual ???

 

[Trimley]

I've yet to read much inside, probably won't until I'm questioning or troubleshooting something anyway.

 

[GreensvilleJay]

good thing is the WSM is free online, bad thing is the wiring diagram is LOUSY....useless as teats on a bull.

 

[DustyRusty]

My BX is only 3 years old and I only use it to mow my lawn. In the past I do recall having a noticable amount of gas escape the fuel cap when I unscrewed it for refuling.

My thought is that as the pump removes fuel from the tank, then the one-way intake valve would allow air to come in to replace the volume that was removed by the fuel being pumped out and creating a slight positive pressure inside the tank.

I don't notice and air escaping when I remove the cap anymore. I didn't know if that was a clue. I have tried to open the fuel cap in an attempt to relieve the vacuum in the line, but that has not worked.

However, when I pull the line off of the pump the vacuum is instantly relieved and fuel immediately gushes out of the inbound line to the lift pump.

I am a novice, but it seems to me that this fuel problem has something to do with venting in the tank, or maybe the fuel line is being pinched off by way of how it is being routed to the pump from the tank?

I do know for sure that the fuel line is oval in shape (not round), when I go to remove it from the inbound side of the lift pump. There is a rush of air into the line when I remove it, and fuel immediately flows out with no evidence of obstrution.

Also, important to note that I have completely removed the primary filter and bridged the line with a 2 sided barbed fitting, so that fuel filter is gone out of the system and is not a factor.

Your tractor uses diesel, not gas!

 

[Jon Baughman]

Your tractor uses diesel, not gas!

Right, I meant the the state of matter (gas / vapor). When I would remove the fuel cap there was a noticable amount of gas vapor that would escape the tank. Like carbonated beverage when you twist off the cap.

Anyway, I don't know if that is normal or not, it is just something that I noticed was not happening anymore. I wanted to mention it because I didnt know if it was relent or not.

 

[Jon Baughman]

Regular preventive maintenance by the owner would deal with the fuel filler cap. It's probably in the owner's manual that no one ever fully reads....
Guess I should finally read my 5 year old owner's manual ???

Thanks for your help. It is very kind to have so many people offer up suggestions to me on this issue. I will continue to pay attention to what condition the cap vents are in and keep working at it. I don't know if that is the issue though.

I really like my tractor. This issue is baffling to me. I have resorted to leaving the hose clamp off of the inbound fuel pump line, so now when the engine dies I reach in underneath and wiggle the fuel line off, release the vacuum and push it back on. The tractor starts right up.

Another interesting data point is that I can tell when the vacuum is built up because I can't hear the fuel pump "ticking" when I am warming the glow plugs up. When the vacuum is released and I turn the ignition key, I can hear the fuel pump ticking (running and pumping fuel) very loud and clear.

I am very sure that the fuel tank outlet is not clogged with debris. When I wiggle that fuel pump line off, fuel will just gush out of it.

 

[Jon Baughman]

Regular preventive maintenance by the owner would deal with the fuel filler cap. It's probably in the owner's manual that no one ever fully reads....
Guess I should finally read my 5 year old owner's manual ???

I checked my book closely and I did not see any mention of cleaning or inspecting the fuel cap. To me that would not seem to be a regular maintenance item.

 

[Jon Baughman]

I notice you didn't mention anything about your piping post injectors?
Suggest maybe you check your fuel overflow line just in case pinched or plugged.
i have never seen one plugged but I have seen pinched lines from shade-tree guys who didn't take care when working on tanks, etc...

This pic from a BX WSM.

View attachment 116120

Thank you for going to the trouble of posting this diagram. That is very helpful and kind of you.

I am familiar with the return line that you are refering to and I did pull it off and and ran compressed air through it. It inflated the fuel tank with air and the excess pressure immediately started bleeding through the outbound vent on the fuel cap.

So I concluded that was not my problem. Maybe I was wrong to conclude that.

I am not a mechanic, but I do understand that air has to enter the fuel tank as the fuel level runs down from operation so as to not develop a vacuum in the tank.

That is why I am going to the tank vent path.