M4900 Slow Throttle Response/Low Power

[Rob. L]

Hello everyone!

I have a Kubota M4900 that has been giving me some issues. I have been trying very hard to get this tractor running better, but apparently I am missing something! Hopefully someone here can help me. When I start the tractor it idles perfectly but when I increase the throttle, it takes about 30 sec to increase to full RPM. When the full RPM is reached- it is lacking power. So much so, it is not able to power any attachments and will die going up even the slightest of inclines. Here is what I have done so far:

Cleaned/Flushed the tank
Replaced fuel filter/fuel lines
Replaced the Fuel Lift Transfer Pump
Replaced old diesel with new

There are a few issues with this tractor that might be related- I don't know. Please excuse my ignorance- I am much more familiar with gasoline engines. 1st, the fuel petcock does not shut off the fuel in the "OFF" position (maybe its letting air in?) and also the injector pump is leaking just a little right where the lines come out of the pump. Its a little hard to start because of that- but not bad.

I talked to an injector pump repair shop and they said that a leaky injector most likely would not cause the power loss/slow throttle. It is on my to-do list for repair/replacement, but I am just trying to get it running better first. Any help in pointing me in the right direction would be awesome!

Thanks,

Robert

 

[1970cs]

How many hours are on it? Sounds like a fuel or governor problem! I would make sure that the the fuel rack in the injection pump has full travel. I would also get a fuel can and hook directly to the injection pump to eliminate a blockage or an air leak.

Pat

 

[Tooljunkie]

Two things you never mentioned, color of smoke from exhaust pipe and condition of air filter.

 

[Tx Jim]

Welcome to OTT
I once owned a M4900 that ran poorly even after installing new fuel filter. It had good fuel flow from tank to water seperator. I located a tiny screen in water seperator fuel shut off valve that was plugged. I cleaned screen and running problem was solved.

 

[Rob. L]

Thank you all for the quick responses! I don't know how many hours are on it, the RPM cable is broken- I have ordered a new one. I wouldn't even begin to try and guess how many, but there are quite a few. There is a small amount of white smoke when it starts and the air filter is new, other than that-no smoke. The fuel rack at the injection pump has plenty of travel.

Pat- Are you suggesting that I bypass the fuel filter and run the fuel line directly to the fuel lift transfer pump?

And Jim- That is some really good info! I had no idea there was a tiny screen in the water separator fuel shut off valve. Would you be able to give me some details on where to find that?

Thanks again for all of the help!

Robert

 

[Tx Jim]

Robert
I unbolted WS assembly from tractor then removed a retaining screw then pulled shut-off valve out of housing to find screen was plugged.

 

[1970cs]

So is it fixed?

Pat

 

[rentthis]

Rob, I have almost the same water/fuel separators on my Kubota excavators. It has been fairly common for them to leak air at the fuel line nipples. One of them is a 90 degree fitting. See if you can turn it with your fingers. If so, it can be temporarily fixed with JB Weld around the base of the fitting. The symptoms are just what you describe. I have had to replace several separators in that the JB Weld thing is only temporary.

 

[Rob. L]

Pat, not quite. I looked up a schematic for the WS and realized that there was a gasket missing that goes in between the fuel shutoff lever and the housing. I have ordered that part and will update when installed.

And Rentthis- I cannot believe this, but I can turn that 90 degree fitting- I just went outside and tried. It doesn't turn freely or anything but it damn sure moves about half a cm to each side. I would have never noticed that- so thank you very much!

When I put on that gasket and now some JB Weld I will keep everyone posted with the results.

-Robert

 

[Rob. L]

I also have one other question for someone who can answer. What is the best way to bleed the fuel out of the lines on this tractor? I was cracking the lines individually at the injector while turning over the engine and waiting for fuel. Is this the correct method? Easier way?

Thanks,

-Robert

 

[1970cs]

Bleed at the the injection pump.

Pat

 

[Rob. L]

Ok, update. Put everything back on- including a new water seperator and still no change in performance at all. With a new tach cable I can see that it's only maxing out around 1600 RPM and nothing more. Very frustrating! Should I start focusing on the injection pump? I don't really know where to go from here.

-Robert

 

[Tx Jim]

I suppose since you cleaned tank,replaced fuel line & lift pump you have good fuel flow from tank to inj pump???? Is tank venting IE try operating engine with fuel cap loose or better yet replaced by a shop towel. How many hrs are on speed/hour meter? It's possible you have governor problems. Try operating engine with fuel return line to tank disconnected. Try operating engine with air cleaner elements removed.

 

[Tooljunkie]

Not that i know much about diesels,but is there a way to check injection timing?
Valve lash allow it to start yet it wont make power?
Just throwing that in since fuel quality/delivery may be ruled out.

 

[1970cs]

Let's go back to what I mentioned on my first post! How did you test the rack on the injection pump? You still have not hooked up an alternate fuel source.

Pat

 

[Rob. L]

I have cleaned the tank, replaced all of the fuel lines and the lift pump and I have good fuel flow from tank to inj pump. I have also ran the tractor without the air filter attached and the fuel cap off- no difference. There are approx 3900 hours on the hr meter- but the tach cable was broken for I don't know how long. I adjusted the governor and that made no difference either. I figured I took care of any fuel flow/air leak issue that it may have had, but maybe I am missing something- I dont know.

1970cs, how do I test the rack on the injection pump?

Thanks again for the replies!

-Robert

 

[Rob. L]

I suppose since you cleaned tank,replaced fuel line & lift pump you have good fuel flow from tank to inj pump???? Is tank venting IE try operating engine with fuel cap loose or better yet replaced by a shop towel. How many hrs are on speed/hour meter? It's possible you have governor problems. Try operating engine with fuel return line to tank disconnected. Try operating engine with air cleaner elements removed.

Jim- 1st off, thanks for all of the help so far! I was thinking more about the possibility of a governor issue over the weekend. When I push the throttle lever forward it only increases the RPM over half of the distance of travel. In other words, from half to full throttle has no effect on RPMs at all. Could this be a governor spring issue? Maybe it could be stretched or something, not allowing it to reach full RPM? Also to note, the throttle has a "loose" feel to it. Ex- when I apply full throttle, the lever backs part of the way down by itself.

Any signs pointing to a governor/linkage issue?

Thanks again,

Rob

 

[1970cs]

I think you still need to run on a clean independent fuel source before going after the injection pump or governor. I don't mean to be rude but this last time I am going to ask the question!

The rack if not fully engaged than you will be under fueled! You have to pull the pump and run the rack manual.

Pat

 

[Tx Jim]

Ex- when I apply full throttle, the lever backs part of the way down by itself.

Any signs pointing to a governor/linkage issue?

Rob

Did you attempt to operate engine with fuel return line disconnected from the tank? Throttle lever backing off could be that friction spring needs more tension by tightening lock nut(key 50). My knowledge of Kubota governors is zero so I think I'm not qualified to reply about governor.

 

[Rob. L]

1970cs, forgot to answer your question earlier. I did hook up an alternative fuel tank directly to the lift pump. The max RPM was still around 15-1600. But when I did that the throttle had less of an impact on the RPM range. For example, when I increased/decreased the throttle, it really didn't change the RPMs. To me, that seems really strange. I will run it without the return line today and see if that makes any difference.

Rob