Kubota B7800 Fuel Solenoid

Miket1961 · Jan 2, 2019

Hello, I'm helping a friend troubleshoot an intermediate problem with his fuel solenoid. It seems to arbitrarily de-energize. We took the dash apart and jiggled wires on the dash and near where they go under the fuel tank. We were unable to find anything definitive. When the solenoid was energized I checked the wire(rd/bk) wire from the key switch to the hot wire on the solenoid and put in a jumper wire from right at the switch to the the plug on the solenoid as a means to troubleshoot . The tractor still stalled out within 15 minutes or so of operating it. I'm having a hard time finding a wiring diagram so that I can properly troubleshoot it. I'd really appreciate any help with this and more so information about the wiring for this circuit.

thepumpguysc · Jan 2, 2019

Regardless of how u have it jumped.. it HAS TO ground THRU the body..
They are a KNOWN problem so its very possible that it does "break down" after running..

TBN Support · Jan 2, 2019

Hi and welcome to the forum!
:welcome:

I'm going to move this thread over to our Kubota section to see if we can find you some answers.

Miket1961 · Jan 2, 2019

Thanks Catherine, that'll probably help me find an answer.
Pumpguysc, I'll check the ground continuity on the other wire and verify if it's open as well. Thanks

LouNY · Jan 2, 2019

Many Kubotas energize the shutdown solenoid to stop,
can you remove the solenoid and run the tractor without it?
Mechanically shutting down and opening the fuel.

Miket1961 · Jan 3, 2019

The tractor will not run unless there is power to the solenoid, so I don't think it will run with the solenoid removed, but I will try it out just to be sure. Thanks

thepumpguysc · Jan 3, 2019

Mike, That's because when u remove the "power".. the solenoid is spring loaded to shut the engine down.. the solenoid plunger pushes on a control rack inside the pump..
IF you REMOVE IT, theres nothing to push the control rack to the "shut-off" position..
SO.. IT'LL RUN.. U just cant shut it off w/ the key switch now..

LouNY · Jan 3, 2019

thepumpguysc said:
Mike, That's because when u remove the "power".. the solenoid is spring loaded to shut the engine down.. the solenoid plunger pushes on a control rack inside the pump..
IF you REMOVE IT, theres nothing to push the control rack to the "shut-off" position..
SO.. IT'LL RUN.. U just cant shut it off w/ the key switch now..

A question for you thepumpguysc is the kubota like many others that energize to run that one wire goes to a pull in coil then the other wire goes to a hold in coil.
Our IH Magnums use this method, my little kubota uses power to stop from a timer when the key is turned of.
Looking at the replacements for a b7800 it looks like it has the pin that moves the internal rack to run and a spring to return to stop?

Miket1961 · Jan 3, 2019

thepumpguysc said:
Mike, That's because when u remove the "power".. the solenoid is spring loaded to shut the engine down.. the solenoid plunger pushes on a control rack inside the pump..
IF you REMOVE IT, theres nothing to push the control rack to the "shut-off" position..
SO.. IT'LL RUN.. U just cant shut it off w/ the key switch now..

You're right pump guy, I didn't think my response through before I replied. I should of said that I don't believe this model to require power to operate the solenoid to shut it off as the only time we've gotten it to run is when we had power to the solenoid. I was not there the last time it stalled. I need to first check if there is power to the solenoid when it stops running and then check the continuity of the ground wire. If anyone has wiring diagram of this circuit I'd appreciate a copy. Thanks for the continued help !

Blondie70 · Jan 3, 2019

A poster above sez it has to ground thru the valve body....if so....why would there be a ground wire ???
Just trying to help out.

Miket1961 · Jan 3, 2019

Blondie70 said:
A poster above sez it has to ground thru the valve body....if so....why would there be a ground wire ???
Just trying to help out.

Overlooked that, thanks. I've been going around in circles trying to find the correct wiring that I'm confusing myself.

thepumpguysc · Jan 4, 2019

Blondie.. IDK.. but it does.. I had a new one in my hand once & was trying to diagnose a "no start" condition..
I had "jumpers" hooked up & it wouldn't pull in.. I "thought" it was bad..
I laid it down on the engine to grab a tool & it "snapped in".. WTH??
So I picked it up & the plunger shot out again.. I grounded it on the pump & sure enough it snapped in again..
So I don't know why.. it just does..

Miket1961 · Jan 4, 2019

thepumpguysc said:
Blondie.. IDK.. but it does.. I had a new one in my hand once & was trying to diagnose a "no start" condition..
I had "jumpers" hooked up & it wouldn't pull in.. I "thought" it was bad..
I laid it down on the engine to grab a tool & it "snapped in".. WTH??
So I picked it up & the plunger shot out again.. I grounded it on the pump & sure enough it snapped in again..
So I don't know why.. it just does..

There a two wires going to this solenoid. I assumed that one was a hot wire and one was a ground. Could it be that one picks up to start and the other is a run coil and the coil grounds through its case to the fuel block. Thanks

orezok · Jan 4, 2019

Heres the wiring diagram for B7800 solenoid.

Miket1961 · Jan 4, 2019

orezok said:
Heres the wiring diagram for B7800 solenoid.

View attachment 585843

Thanks so much !!

7Jetboy · Jun 21, 2021

Miket1961 said:
Hello, I'm helping a friend troubleshoot an intermediate problem with his fuel solenoid. It seems to arbitrarily de-energize. We took the dash apart and jiggled wires on the dash and near where they go under the fuel tank. We were unable to find anything definitive. When the solenoid was energized I checked the wire(rd/bk) wire from the key switch to the hot wire on the solenoid and put in a jumper wire from right at the switch to the the plug on the solenoid as a means to troubleshoot . The tractor still stalled out within 15 minutes or so of operating it. I'm having a hard time finding a wiring diagram so that I can properly troubleshoot it. I'd really appreciate any help with this and more so information about the wiring for this circuit.

I was going through the same thing with my B7800! It would start then just quit. When I tried to restart, the engine would turn over but not start. The stop solenoid was not engaging which you'll hear when turning the key - it clicks and is very audible. The tractor would work fine for a while then it would act up. If I left the tractor for a few minutes and came back to it, it would start and run fine at times. Then it would run and turn off arbitrarily and I'd have to wait for the stop solenoid to engage so I could restart the engine. After changing a few parts, I got behind the dash of the tractor. There was a mouse nest in there and I cleaned that out. Fortunately, there was no wire damage. I checked everything behind the dash, changed the relay, still did not fix the issue. Then, with the key turned to the run position, I jiggled the controller (it's behind the fuel gauge) and the stop solenoid engaged (clicked) and the tractor would start. So, I purchased and replaced the controller ($155) and the issue has been fixed!! Been running without issue since then!

Kingston1960 · Jun 22, 2021

7Jetboy said:
I was going through the same thing with my B7800! It would start then just quit. When I tried to restart, the engine would turn over but not start. The stop solenoid was not engaging which you'll hear when turning the key - it clicks and is very audible. The tractor would work fine for a while then it would act up. If I left the tractor for a few minutes and came back to it, it would start and run fine at times. Then it would run and turn off arbitrarily and I'd have to wait for the stop solenoid to engage so I could restart the engine. After changing a few parts, I got behind the dash of the tractor. There was a mouse nest in there and I cleaned that out. Fortunately, there was no wire damage. I checked everything behind the dash, changed the relay, still did not fix the issue. Then, with the key turned to the run position, I jiggled the controller (it's behind the fuel gauge) and the stop solenoid engaged (clicked) and the tractor would start. So, I purchased and replaced the controller ($155) and the issue has been fixed!! Been running without issue since then!

Thank you 7Jetboy
Your Information was very helpful

Henro · Jul 5, 2021

Kingston1960 said:
Thank you 7Jetboy
Your Information was very helpful

I believe I read somewhere that the later produced models of the B2910 and B7800 use a different electrical setup with an OPC (operator presence control) module that controls the fuel cutoff solenoid. This caught my attention as I have a B2910.

If my memory is telling the truth, one needs to make sure which version he has when troubleshooting electrical problems.

Mine does not have the OPC module fortunately. It is a small plastic box under the dash somewhere, with a number of wires going into it. I want to think if the tractor has a seat presence switch this may indicate it’s a model that has the OPC unit.