Another M6800 Fuel System problem

[Headrc]

Hello to everyone, I am new to this forum as of this morning but have visited it several times over the ownership of my Kubota M6800 over the past 20 years for repair and maintenance information. Thank you all for that.

I now have a new fuel system problem and it appears I am going to have to go deeper into it than the usual air purging procedure. The tractor sat for a couple of weeks after using it flawlessly for a couple of days with no problem. However, I proceeded to use it a couple of days ago and upon starting it, it would not accelerate to its normal running RPMs and after several tries at raising the the RPM's it final reduced to a very low idle and stalled out. It now will not start at all. My suspicion is air in the fuel system but using the usual air purging procedure with the fuel filter hand pump does not solved the problem.

I have found a couple of threads on this forum with a similar problem with diagrams of the fuel system and discussion of digging deeper into fuel lines and air problems. However none of the diagrams give the item description for each of the fuel lines, air vents etc. i think this would be helpful to me. Can anyone post the fuel system diagram with the component descriptions for me? And of course if anyone can advise further on purging air out of the system other then the one i have been trying it would be most appreciated. Thank you in advance! Richard

 

[Tx Jim]

Welcome to the OTT
I don't have a diagram of the fuel lines on a M6800 BUT I once owned a M4900 that acted similar to what you described. A local Kubota dealer service manager advised me to check for a clogged screen on fuel cut-off valve in water separator housing. I removed fuel shut-off valve retaining screw the pulled valve out of housing. The SM was correct the tiny screen was clogged. Long story,short story after cleaning screen & reassembly,bleeding fuel system engine operated fine.

 

[Headrc]

Thanks ...sure would be great if the problem is that simple. That diagram would sure help with little things like this ...so that screen is actually behind that shutoff cock retaining screw?

 

[Headrc]

OK ...stupid me. I found diagrams on Kubota's website ....but candidly I do find any type of filter screen behind that shutoff petcock on the water separator.

 

[Tx Jim]

IIRC the tiny screen on M4900 water seperater fuel control valve isn't shown in parts diagram either BUT that didn't keep that screen from being clogged blocking fuel flow. Back when I served as an equipment dealer service manager I was taught to check the easy things 1st. . Removing the screw, sliding valve out & peeking at clogged screen was fairly easy. Plus I've read where fuel flow has been stopped by clogged passages in water separator housing. Would you like to speculate what item B is because it's not listed in parts descriptions that I read

 

[Headrc]

Yeah well I saw that and wondered ...so that is what it is. thanks.


And now another question comes up looking at the Kubota web site diagrams. There is not a complete fuel system diagram that I can find that incorporates the fuel fuel filter, fuel pump, water separator and injector pump. Is this the order....fuel filter then fuel pump then water separator then injector pump? Thanks to anyone who can help.

 

[Tx Jim]

I didn't state item B was the screen I referred to but I just implied it could be a screen because it wasn't identified in parts descriptions. IMHO Kubota engineers went out of there way to make the fuel hose routing from tank to injection pump more complicated than necessary.

 

[whitetiger]

Yeah well I saw that and wondered ...so that is what it is. thanks.


And now another question comes up looking at the Kubota web site diagrams. There is not a complete fuel system diagram that I can find that incorporates the fuel fuel filter, fuel pump, water separator and injector pump. Is this the order....fuel filter then fuel pump then water separator then injector pump? Thanks to anyone who can help.

The flow is Fuel Tank to Water Separator to Lift Pump to Fuel Filter to Injection Pump. See attached PDF.

 

[Headrc]

Thanks that flow diagram helps me a lot in better understanding the system. where di you find that diagram BTW?

 

[Headrc]

Sooo ....I am up and running. It appears that a dirt Dauber plugged up the gas tank vent ...and cause havoc with air in the fuel system. Thank you all for your help!

 

[whitetiger]

Thanks that flow diagram helps me a lot in better understanding the system. where di you find that diagram BTW?

It's from the Work Shop Manual.

 

[Headrc]

So ....my problem persists. After fixing what I thought was the problem with the dirt dauber in the gas tank air vent ....I still have a problem. And I now see what it is ....for some reason that hand pump on the top of the fuel filter assembly is being pulled into the down position when the tractor sits dormant for several hours. It then will not go back into the up position ....and induces air into the system. Has anyone else encountered this problem? Any fixes other then replacing the unit? Which of course looks like it will be a pain top do.

 

[Gus1957]

I'm having various M6800 problems too. Did you resolve this and how? TY