Kubota KX41 revs dropping when hydraulics are activated

[K5lwq]

OK. So yes it's very different at lower RPM.
At 1500RPM there is very little drop - drops to 1400 under the heaviest load.
At 2000 RPM it drops to 1800ish.
I'm guessing that this would point us back to fuel rather than hydraulics? Or not necessarily if higher throughput of oil in hydraulics at higher RPM amplifies the effect of any blockage/restriction in hydraulic system?

The system will reach full pressure with the engine at idle. It just takes slightly longer to get there. So the RPM drop you describe at 1500 is what I would expect. I would think the curl and maybe the boom would have a restrictor installed to slow operation down on purpose. This could be why there is any drop without a load.

Based on this information, I would say yes the hydraulic system most likely is not the issue. Seems the problem is on the higher end of the power curve. Of course knowing pressures would be nice but I think you can rule out hydraulics.

If this engine was computer controlled, then I would think it is limiting the RPM for some reason. Not knowing if it has a ECM I have to agree fuel is a likely issue. In this cause I think the fuel system is producing enough flow for good power at lower RPM. But as fuel demand increases, the system can’t keep up. This could explain the slow return to high RPM.

I think Jerry has the right idea. I might would run a temporary fuel line from a fuel can straight to the lift pump. This would bypass the tank and see if it acts differently at higher RPMs. If the same result then I would try a cheap electric fuel pump and run a line straight to the injector pump. Then try high RPM again. At some point it will narrow down the problem area and give you a better bead on the issue.

 

[Godhungry777]

Look

Look at my comment at the Orange Tractor Talk Forum. The load that you are putting on the machine by curling the bucket is very small, so I think your problem is fuel flow related. Remove the line that goes to the Injector Pump. Crank the engine and you should have a steady full stream of fuel from that line. If it dribbles, is intermittent, and is not a full stream, check the lift pump and the filter head as well as the tank outlet. If you had a dirty fuel tank, you might not have gotten all the crap and corruption out of the system.

How's this flow (see video)?

 

[K5lwq]

Everything I can find says that engine is rated for 2300 RPM not 3000. What if you drop the rpm to 2300 and see how it works.

Someone may have adjusted the throttle stop thinking they were increasing power. Or could the governor be going full bore without a load causing a increase in RPM?

After watching the first video again and it was started at max RPM, at the start it was about at 2300. Then it started over revving slowly until it reached 3000 RPM.

If it revs high enough for the valves to start floating you would lose power. If fuel is not a problem, then I would start investigating the proper max RPM setting.

 

[kwbretired]

Don’t some injection pumps have a screen on the inlet? Is it could be partially plugged.

 

[Godhungry777]

Everything I can find says that engine is rated for 2300 RPM not 3000. What if you drop the rpm to 2300 and see how it works.

Someone may have adjusted the throttle stop thinking they were increasing power. Or could the governor be going full bore without a load causing a increase in RPM?

After watching the first video again and it was started at max RPM, at the start it was about at 2300. Then it started over revving slowly until it reached 3000 RPM.

If it revs high enough for the valves to start floating you would lose power. If fuel is not a problem, then I would start investigating the proper max RPM setting.

Yeah, you're right - kind of.
Max RPM for the D1105-BH in the KX41 is 2600RPM.

Though, from what I've seen, the D1105 comes in various configurations for different applications and max RPM ranges from 2300-3300.

 

[K5lwq]

Yeah, you're right - kind of.
Max RPM for the D1105-BH in the KX41 is 2600RPM.

Though, from what I've seen, the D1105 comes in various configurations for different applications and max RPM ranges from 2300-3300.

I see what you are saying but notice the HP difference between the two you highlighted. That is not achieved by increasing RPM alone. It requires a different tune. Could be a different injector pump or the fuel turned up on the same pump.

I think in your case the RPM needs to be no more than 2600.

 

[Jerry/MT]

How's this flow (see video)?

See my comments on OTT

 

[oldnslo]

When you tested Pressures at lower RPMs did the pressure drop as soon as you stopped activating that function? If yes does pressure also drop the same way at higher RPMs? Is there a certain RPM where revs drop and doesn’t recover? I.e. 2,000 is OK 2,300 drops..

I was going to study the hydraulic schematic in post #6 in greater detail but it is no longer there.

 

[Godhungry777]

When you tested Pressures at lower RPMs did the pressure drop as soon as you stopped activating that function? If yes does pressure also drop the same way at higher RPMs? Is there a certain RPM where revs drop and doesn’t recover? I.e. 2,000 is OK 2,300 drops..

I was going to study the hydraulic schematic in post #6 in greater detail but it is no longer there.

 

[4570Man]

The vast majority of stalling issues are caused by fuel starvation. Does the engine blow black smoke or otherwise act like it’s working hard when it’s slowing?