Kubota L4600

[Laner7]

Hi, new to the forum! Just recently my kubota L4600 has been underpowered. I just recently changed all of the fluids and filters and the problems persists. When it’s parked it runs fine. As soon as I start to drive the rpm’s fall to around 1500 and every once in awhile I’ll hear a knock. There’s some black & white smoke on start up, but it goes away once it’s started. Any help would be appreciated. Tractor has 457 hours

 

[North Idaho Wolfman]

Hi, new to the forum! Just recently my kubota L4600 has been underpowered. I just recently changed all of the fluids and filters and the problems persists. When it’s parked it runs fine. As soon as I start to drive the rpm’s fall to around 1500 and every once in awhile I’ll hear a knock. There’s some black & white smoke on start up, but it goes away once it’s started. Any help would be appreciated. Tractor has 457 hours

Take a video of it starting, and running and when it bogs down.
Post the video on Google share or YouTube and give us link to see it.

 

[Laner7]

Okay, I’ll try to figure out how to do that. Thanks

 

[D2Cat]

Sure sounds like a fuel problem. Could be a restriction in the tank. You installed new fuel filter?

 

[Laner7]

Sure sounds like a fuel problem. Could be a restriction in the tank. You installed new fuel filter?

yes sir, new fuel filter. It runs normal when parked, but as soon as I start to drive it bogs down and will hang around 1,000 to 1500 rpm’s. As soon as I let off the gas it revs back up to normal. It will have a knock sometimes, but doesn’t happen every time.

 

[GrizBota]

By “let off the gas”, do you mean let up on the treadal (HST pedal)? Or the engine speed setting on the dash board?

 

[D2Cat]

Did this situation begin after something you did, like add fuel? Do you have good fuel flow at the filter when it was changed?

 

[North Idaho Wolfman]

Is the parking brake on?
It's happened to a lot of us!

 

[Creature Meadow]

Is the parking brake on?
It's happened to a lot of us!

Indeed it has for me most often when I back off the trailer which is the only time I use it.

Excellent thought even if not the problem.

 

[Laner7]

Y

By “let off the gas”, do you mean let up on the treadal (HST pedal)? Or the engine speed setting on the dash board?

Yes, after I let off the pedal is revs back to normal

 

[Laner7]

Did this situation begin after something you did, like add fuel? Do you have good fuel flow at the filter when it was changed?

no sir, it was running good all day and then it started happening. So my first thought was dirty fuel filter and installed a new one and the problem persists. It has good flow from the fuel tank to the bowl and good fuel to the injectors

 

[Laner7]

Is the parking brake on?
It's happened to a lot of us!

I have had that happen to me as well and no, I made sure the brake was off.

 

[North Idaho Wolfman]

good fuel to the injectors

How do you know this?

 

[Laner7]

How do you know this?

True. I could be wrong, but I believe I pulled the hose off from the fuel pump to make sure it’s receiving fuel.
I’m attaching a picture of my tractor. The red circle is the line I pulled to make sure it was receiving fuel

 

[North Idaho Wolfman]

To know you were getting good fuel to the injectors you would crack these lines (yellow) at the injector end for each injector, but don't do that yet.
Try this:
With the tractor running, Take the vent line off at the blue mark, then open the jet start valve (purple) and see if you get good flow.

 

[Laner7]

To know you were getting good fuel to the injectors you would crack these lines (yellow) at the injector end for each injector, but don't do that yet.
Try this:
With the tractor running, Take the vent line off at the blue mark, then open the jet start valve (purple) and see if you get good flow.

View attachment 113247

Okay, thank you for the help. I had to leave for work and won’t be back to mess with it for about a week. I’ll try that out when I get back.
1.) Say I do all of that and have good flow… what would be the next step?
2.) Or say if I do all of that and I don’t have good flow… what would be the next step?

reason I ask those questions is so if I need to order new injectors, fuel lines or fuel pump, etc. I can already do that so that I have that on hand when I’m working on it again to get it going.

 

[North Idaho Wolfman]

It's hard to say what the exact cause of the issue is.
If it lack of flow, it's either lift pump or a blockage in the line, filter or tank.
If it's good flow, could be pump or injectors, other tests will need to be performed.

 

[Laner7]

It's hard to say what the exact cause of the issue is.
If it lack of flow, it's either lift pump or a blockage in the line, filter or tank.
If it's good flow, could be pump or injectors, other tests will need to be performed.

I appreciate the help. I’ll give it a try when I get back to the ranch and report back!

 

[Laner7]

I still haven’t been back to the tractor to try what you suggested. But I talked to my local kubota mechanic and he basically had no idea what the issue could be. But he seemed to really be leaning towards a hydraulic issue and then said it could also be a safety switch problem after I suggested that to him. He doesn’t think it’s a fuel problem. Does this seem right? He seemed all over the place with his responses. So I’m not sure how much I trust him.

 

[Laner7]

Update: i put seafoam in the tank & I tried what you suggested and ran the tractor with the vent line off and opened the jet start valve. Should it be a full constant stream? Or spitting fuel?
regardless after doing this the tractor now runs fine? Ran it for 2 hours without any problems.