Kubota lift pump

[alexanderfoti]

HI all

Having running issues with my D850, primarily, it wont run very well at idle, but at higher rpm's its ok.

I am suspecting the lift pump is not flowing well at low rpms, any idea how much its meant to flow? I get a small squirt at tickover on idle, but its only a few drops, really not a huge amount.

None of my engine documentation hints at how much it should flow etc.

[Tetronator]

I have removed mine on my D722, (It hasn't run yet), figured that having the fuel tank directly above the engine will suffice.
Seen a couple D722s run without so should be fine.

Will tell if its a success or not.

[alexanderfoti]

Maybe I will try that. It does wonder why they would put one on of its not needed?

[Tetronator]

If the fuel tank is xx feet away or in some basement or another/below the engine you'll need someway to get the fuel to the engine.

[alexanderfoti]

True. I will bypass it and see what happens.

[klondikekid]

My D950 runs fine without the pump, if that helps

[pietenpol2002]

It does wonder why they would put one on if its not needed?

I've read that Kubota incorporates a low pressure pump (electric or mechanical) to supply a consistent pressure to the injection pump as a part of their fuel delivery system design. That said, there are Kubotas that apparently function quite well with only gravity feed.

[bf109v7]

I have a traktor with a 3 zylinder Kubota, the tank is higher than the eginge and there is no lift pump. And that is how it came from the factory.
Alex

[gilburton]

Maybe I will try that. It does wonder why they would put one on of its not needed?

It all depends what vehicle or installation the engine came from.
For instance if it came from a fridge trailer the fuel tank is usually down below on the chassis or if a Z482 comes from an Aixam car they will need a pump.
On motorcycles a lot of them now have fuel pumps either because of the EFI or sometimes the carbs or injector bodies are high up under the tank so gravity isn't enough.
A simple diesel engine should run on gravity as long as the injector pump is well below the tank.

[alexanderfoti]

True, as I'm not sure where it came from it must be that the original tank was lower.

[klondikekid]

If the pump is defective, maybe it's an obstruction now, just a thought...

[Mouse]

If the pump is defective, maybe it's an obstruction now, just a thought...

Worth checking.

I've run the z482 with and without lift pump and they work equally well. I've also run a z482 with no lift pump and the tank below the pump. The big advantage is that priming is much easier with the lift pump on the rare occasion I run out of fuel.

As far as I'm aware all mechanical pumps are positive displacement pumps so that once primed will work properly as they provide their own lift suction.

I have has issues with partially leaky fuel pipes and joints where the 'leak' is not enough to leak fuel out when the engine is off but when running the suction from the pump / lift pump is enough to suck air in through the leak and cause low RPM running and starting issues. Very hard to detect as you cant see through fuel lines that are not clear so you cant see the bubbles. Maybe pull the return tube off and look for bubbles in the return flow with the engine running. Maybe worth adding to your fault finding investigations.

[thinking aloud] You do have a breather in the tank cap ?