# Kubota d902 losing power



## Josephlister (Aug 22, 2021)

I've got a gravely 460 pro turn with a 3 cylinder Kubota d902 diesel. I got it for a good deal because it couldn't pull itself up a hill when cutting. It's only got 680 hours. If you're going up a hill or even cutting slightly thick grass, I mean wouldn't even bog down a weed eater very much, it starts bogging. If I crawl as slow as the more can go it won't bog. Unless I'm in decently thick grass. I was told they had water in the fuel, they replaced the fuel filter, clean the tanks and lines. When I got the mower and it was still losing power there was also an alarm going off because the water temperature sensor wire was broke. I fixed that and the alert light stop blinking and the shutdown light continued flashing and the beeper kept going. The beeper beeps before you've even started the mower when the key is in the run position. Anyway I pulled the fuel filter and it was Rusty and didn't look so good so I replaced it and it didn't make a difference. Both tanks have fresh diesel in them. No smoke when the mower starts bogging and one more thing I noticed is even with the blades off if you try to take off too quick it bogs down. Almost to the point of shutting off. I know that this mower has a lot more power than it does right now because from the factory you can buy it with a 72 inch deck. Same motor. Mine has a 60 inch deck and can't pull itself up a hill when cutting. I have not pulled the tanks and clean them or anything like that. Does the tank switch valve have a screen in it that could be plugged? The inline filter has diesel in it and the fuel pump pumps. I don't believe it's a head gasket because the coolant is clean and stays at a good level. Some people say the exhaust could get plugged but wouldn't that make it bog all the time? If you're not moving fast with the blades off it doesn't bog at all. I do notice that at lower RPM with the blades off just trying to move there's a little bit of a knocking sound. But it's a diesel and it sounds like diesel noises to me. My truck does the same thing if you take off by dumping the clutch at idle. Sounds like regular diesel noises. Anyway sorry for rambling on for so long and I'm just hoping someone can give me a good place to start. Should I pull the tanks, or replace the tank switch valve? I work on my truck on my own and I know a fair bit about diesels but I'm not familiar with a Kubota lawn mower engine. Any help is appreciated. Thanks.


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## thepumpguysc (Jan 25, 2015)

If it has an electric supply pump that feeds the injection pump.. disconnect it at the inj pump inlet.. 
Route the hose into a bucket..
Turn the key ON.. that should start the electric supply pump..
Watch the flow for a minute or two..
It should be a heavy, steady stream..
Once it passes or fails that test, look into the bucket for any debris..
That’ll let u know your next steps..
replace the supply pump, remove the fuel tank and clean.. replace the rubber fuel hoses..
One more thing to check is..
Remove the air cleaner and box before u do anymore running tests..
I’ve seen the plastic air hose get sucked together..
Good luck


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> If it has an electric supply pump that feeds the injection pump.. disconnect it at the inj pump inlet..
> Route the hose into a bucket..
> Turn the key ON.. that should start the electric supply pump..
> Watch the flow for a minute or two..
> ...


I hate it but I'm starting to think this thing is running at full capacity. I took the muffler off and checked fuel flow and took the air cleaner off and it still bogging when you put it under a load. Good fuel flow at the injection pump. Muffler was not clogged, and the air filter hose is not collapsed. It was exactly the same with everything off as it was with everything on. Unless I have a bad injector or something and maybe one cylinder ain't firing right. It just doesn't seem right considering it can take a 72 in deck but it's having trouble with a 60. Doesn't make much sense to me. It starts so good even cold in the morning. I can twitch the key as fast as I can and it'll still start. Is there any way to check my injectors? I would think it would be smoking if there was a problem but there's no smoke. The instant it starts there's a tiny little puff of white smoke and then it's gone and it's smooth from there. I guess I need to check my injection pump pressure and my injectors next.


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## BigT (Sep 15, 2014)

Try this.... My neighbor used to come by about every 2-3 months, saying his Kubota had lost power. What I did was, with the engine running, I would crack open each injection line, at the injector, one at a time, and let it purge diesel (maybe some air...I dunno??). When I got done, I would tell him to go out into the pasture and see how it ran. It always regained its power. I never did figure out what was wrong with that tractor, but the solution was simple.


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## BigT (Sep 15, 2014)

Deleted double post... sorry about that!


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## thepumpguysc (Jan 25, 2015)

Definitely give bleeding at the injectors a try.!! But.. if that doesn’t work, u could try giving it more fuel..
The max fuel screw is located inline w the pump control rack.. either to the left or right of the injection pump ..
More than likely it’ll have a tamper proof cap on it..w a wire seal on it.
I’ll leave getting it off to u..
Once uncapped, u usually have to back it out..PAY ATTENTION TO HOW FAR
u backed it out.. I would go 1 FULL TURN. THEN give it a test run..
What u DONT WANT TO HAPPEN IS it ROLLING BLACK SMOKE..!!
That’s just unburnt fuel rolling outta the stack and washing down the cylinders..
Give that a try..& good luck.


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> Definitely give bleeding at the injectors a try.!! But.. if that doesn’t work, u could try giving it more fuel..
> The max fuel screw is located inline w the pump control rack.. either to the left or right of the injection pump ..
> More than likely it’ll have a tamper proof cap on it..w a wire seal on it.
> I’ll leave getting it off to u..
> ...


There's a screw on the left and the right which one is the adjustment. They both have a little cap on them and one of the caps can spin.


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> Definitely give bleeding at the injectors a try.!! But.. if that doesn’t work, u could try giving it more fuel..
> The max fuel screw is located inline w the pump control rack.. either to the left or right of the injection pump ..
> More than likely it’ll have a tamper proof cap on it..w a wire seal on it.
> I’ll leave getting it off to u..
> ...


All the videos I'm finding with a similar injection pump say it's the screw on the front side of the motor with the spinny cap on it. There's also a governor screw to make the motor rev up higher. I don't know anything about with the previous owners could have done so I don't know if they turned it in for whatever reason not knowing what they were doing. But I will try turning the fuel up a little bit and see if it makes a difference


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> Definitely give bleeding at the injectors a try.!! But.. if that doesn’t work, u could try giving it more fuel..
> The max fuel screw is located inline w the pump control rack.. either to the left or right of the injection pump ..
> More than likely it’ll have a tamper proof cap on it..w a wire seal on it.
> I’ll leave getting it off to u..
> ...


I turned the fuel up. It had one of those dummy screws on it. I backed it out but it would only go out a few turns and then you have a screw on the front you tighten down to keep it at that spot and at some point that nut won't thread anymore so you can only go out so many turns before it won't work anymore. I adjusted it out the few turns that it would let me and made sure I wasn't getting any black smoke under load which it still doesn't smoke at all the only smoke I saw was when I go from idle to full throttle there's a tiny little puff of white smoke and then it clears up and it's fine but with that and the 2 to 400 RPM increase on the throttle that I adjusted as well I tried to do what I normally do and take off really fast to see how far the front tires will come off the ground normally they would only come up six inches or so and the mower would bog down and fall back down. I tried it again and the wheels came like three feet off the ground. I got scared I was going to flip over there for a second. But there's no black smoke I made sure of that when I stuck it in some heavy grass I had someone watching and there was no smoke at all. I think I got four so turns out on that fuel screw. I tried a couple to start and it felt better but it still didn't feel like it was there so I went ahead and took it as far out as it would let me. The mower feels great now. Thanks for y'all's help I really appreciate it


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## thepumpguysc (Jan 25, 2015)

Good Lord.!!! 
Whatever Floats yer boat. Lol


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> Good Lord.!!!
> Whatever Floats yer boat. Lol


Well as I said before when you're cutting you couldn't even go up a slight incline without the motor bogging down to the point of shutting off. The previous owners have done all kinds of things they probably shouldn't have done. Trust me I don't want to blow the motor up I just wanted to have the power it should have from the factory. And if it can pull a 72 inch deck it should be able to pull a 60 inch deck. There's still a lot of adjustment on that throttle cable but I'm not going to mess with it. As long as it can keep the RPMs up when I'm cutting then I'm fine with it. I don't need a ridiculous bushhog. Another thing that it would do is when you engage the blades the motor would bog way down and take a few seconds to catch back up. I felt it shouldn't have had so much trouble engaging the blades. I'll post a video on YouTube and send you a link on how it is now so y'all can tell me what you think.


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## Josephlister (Aug 22, 2021)

thepumpguysc said:


> Good Lord.!!!
> Whatever Floats yer boat. Lol


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## HarveyW (Sep 15, 2014)

Sounds really good to me.


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## Josephlister (Aug 22, 2021)

Turns out the reason it didn't start smoking from adjusting the screw all the way out cuz I never adjusted it. I took the protective cap off and there was a 10 mil nut on the outside and the inside. I did not however know that the outside nut was another protective cover and I thought that was the adjustment screw. The really I didn't adjust to feel at all all I did was turn the RPMs up a little bit. That outer screw is the cap over the Flathead. So I did not adjust the fuel at all lol I found this out because I found another video about it and watched him do it from the beginning. Well anyway I guess it doesn't matter. I think it just wasn't getting the RPMs it was supposed to.


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## HarveyW (Sep 15, 2014)

Max rpm spec for your Kubota D902 engine is 3500 rpm.


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## Josephlister (Aug 22, 2021)

HarveyW said:


> Max rpm spec for your Kubota D902 engine is 3500 rpm.


Just to see I put the throttle cable back to the factory spot but I dont have a a tacometer. I adjusted the fuel out a little bit and when I engage the blades there's a puff of black smoke then it clears up. Is that too much fuel? It smoking when first engaging the blades? Should it not smoke at all? Even when engaging the blades? I will say when I adjust the fuel to the point where it smokes a puff of black smoke when I engage the blades the mower doesn't even notice I turned the blades on. Like it's got way more power but if that's too much fuel I don't want to hurt anything.


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## HarveyW (Sep 15, 2014)

I think that should be OK. Wait for thepumpguysc to comment


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## Josephlister (Aug 22, 2021)

HarveyW said:


> I think that should be OK. Wait for thepumpguysc to comment


It was a pretty visible cloud. It was definitely a little bit black but it only happened when I first engaged the blades and it cleared up. I did play with the adjustment some more just to see how the motor reacted with more or less fuel. When I turned it down to where it was factory and engage the blades the mower would bog down and take about 3-4 seconds or so to get caught back up to speed. When I turned it out about a turn and a half or so from factory I get a small cloud of black smoke right when I engage the blades but the mower never bogged down from engaging the blades. It stayed at about the same RPM and if it dropped any it was very hard to tell. But if I get a cloud of smoke from engaging the blades I would probably get a pugf of smoke when I stuck it in some thick grass too I would assume. I'll have to try it out a little bit. I put it at one turn out and I get a somewhat visible cloud of very dull black smoke. There's not a whole bunch of black in it but it is still a darker color. It's definitely not white. And when I engage the blades it takes about a second to catch up to RPM maybe less. I'm at the point where I don't know if I want to leave it there or put it back at the turn and a half. It definitely seemed to have more power at a turn and a half but I'm sure every time I put it under a good load it'll probably smoke a bit.


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## Josephlister (Aug 22, 2021)

Here's a short video of it


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## SidecarFlip (Mar 25, 2021)

You need to engage the blades at a MUCH LOWER RPM. All you are doing is wearing it the clutch and belts. Smoke ain't much.


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## Josephlister (Aug 22, 2021)

SidecarFlip said:


> You need to engage the blades at a MUCH LOWER RPM. All you are doing is wearing it the clutch and belts. Smoke ain't much.


Never thought about that. I'll find a happy spot for it. So the smoke is ok?


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## SidecarFlip (Mar 25, 2021)

It's mechanically injected just like my big Kubota's are so when you open the throttle, the pump gives it fuel to the setting it's at and as the motor spools up it smokes. Now if you are mowing with it and is smokes a lot, it's getting too much fuel so you need to back it down a little. Excess fuel equals excessive combustion chamber temps and that is no good. When I work my M's hard, they smoke a bit but not excessively.


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## Josephlister (Aug 22, 2021)

SidecarFlip said:


> It's mechanically injected just like my big Kubota's are so when you open the throttle, the pump gives it fuel to the setting it's at and as the motor spools up it smokes. Now if you are mowing with it and is smokes a lot, it's getting too much fuel so you need to back it down a little. Excess fuel equals excessive combustion chamber temps and that is no good. When I work my M's hard, they smoke a bit but not excessively.


Ok that makes me feel a little better about it. As long as it only smokes when under heavy (like engaging blades or hitting really thick grass) load its ok. As long as it's not smoking unloaded everything is fine correct?


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## SidecarFlip (Mar 25, 2021)

How is the air cleaner?


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## Josephlister (Aug 22, 2021)

SidecarFlip said:


> How is the air cleaner?


Good and clean. I'm going to get a new one anyway though. I even tried running it with no filter on it just to see if it made a difference and it did not. I also pulled the muffler which did nothing.  Adjusting the fuel made the mower fuel completely different. When I first got the mower it was losing power and that's why I got it so cheap and that was one of the first things I checked. Along with the fuel filters. The mower only has 680 hours on it. It's supposed to be able to pull a 72-in deck from the factory so I knew something wasn't right.


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## SidecarFlip (Mar 25, 2021)

I'd suggest installing an exhaust pyrometer in the exhaust manifold close to the cylinders. If you exhaust temperature exceeds 1500 degrees under load, your pistons are at risk. Alloy pistons don't survive well at 1500 degrees.


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## Josephlister (Aug 22, 2021)

SidecarFlip said:


> I'd suggest installing an exhaust pyrometer in the exhaust manifold close to the cylinders. If you exhaust temperature exceeds 1500 degrees under load, your pistons are at risk. Alloy pistons don't survive well at 1500 degrees.


I can prob find one on Amazon in a kit for pretty cheap I'd assume. I'll look in to it.


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## JBob (9 mo ago)

I realize this is an old post. I have the same issue. Did you resolve the low power issue?


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## pogobill (Jan 31, 2012)

Welcome to the forum JBob. Seems Josephlister hasn't been here for 8 months. 

You may want to start a new thread of your own and ask the questions.


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