Kubota KX41 revs dropping when hydraulics are activated

[Jerry/MT]

Does this machine only have one pump? I thought the schematic showed 3 separate pumps P1, P2, and P3.

It did not look like unstable rpm's to me from the video. I'll take your word for it that it is. That would point to a problem with the governor in the IP since you supposedly have the hydraulics disconnected.

 

[Godhungry777]

Does this machine only have one pump? I thought the schematic showed 3 separate pumps P1, P2, and P3.

It did not look like unstable rpm's to me from the video. I'll take your word for it that it is. That would point to a problem with the governor in the IP since you supposedly have the hydraulics disconnected.

3in1

Instability is probably the wrong description. You're right that it's stable once it reaches the throttle setting. What I'm referring to is that when you set the throttle, it takes so long for the revs to get up or down to where you've set it that you need to keep make adjustments once it gets there to try get it to set at 2300RPM.
A good chunk of the 2 minute video is me adjusting the throttle just trying to get it to 2300RPM.

 

[K5lwq]

Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.

• It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
• It still takes for ever to increase or decrease RPM when the throttle is adjusted.

So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:

• emptied and cleaned fuel tank (had water, rust and gunk)
• replaced fuel filters (clogged with water and gunk from tank)
• replaced fuel lines (lines were brittle) -
• tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
• Tested fuel slider rail. Full and free movement.
• had injectors tested - tested ok
• bled injector lines
• replaced engine oil and oil filter
• replaced thermostat and coolant (thermostat was stuck open)
• air filter had already been replaced - exhaust is clear
• checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

There is a sharp guy on this forum that goes by @thepumpguysc. I think he may have some suggestions if he sees this thread.

 

[ddbackhoe]

There is a sharp guy on this forum that goes by @thepumpguysc. I think he may have some suggestions if he sees this thread.

I was wondering why he had not chimed in. Wouldn't hurt to pm him.

 

[number two]

TBN has been down a lot for me this week.

 

[thepumpguysc]

Thanks for thinking about me..
We’ve chatted about this on another forum..with no improvement, sorry to say..

 

[ddbackhoe]

Thanks for thinking about me..
We’ve chatted about this on another forum..with no improvement, sorry to say..

Well, whats left? If fuel delivery is ok, timing is good, valve lash is ok….My next thought would be to use an endoscope camera to look at piston walls, valves and valve seats. Other guesses?

Links posted for suggestions only. Your usage may vary

https://www.amazon.com/Endoscope-Borescope-Inspection-Waterproof-Semi-Rigid/dp/B09NVYXTG5

 

[thepumpguysc]

I don’t think the pump has been apart and put back together by a “qualified” inj pump tech.??
He also has the max fuel and torque screw completely out.. there’s no starting point..
It’s my “guess” is, that between the rpm’s and max fuel, he’s overcoming the gov springs with any load applied..
It’s just a guess mind you..

 

[aesmith]

What strikes me is how slow that engine revs up. Something like 40 seconds or so from when he let go of the throttle until the revs stopped rising? We have the same machine, KX41 with D1105BH engine. I'm sure it doesn't take more than a second or so, maybe even less to rev up when I adjust the throttle.

 

[hayden]

It's definitely the governor. I don't know how it works on that particular engine, but no governing is happening.