Kubota kx121 cranks but won't start

[AGENT86]

Hi all. New guy here. I need some help. My friend has a kubota kx121 up here that was running fine. The hydraulic tank was low (I just got up here recently, was not yet doing maintenance on the equipment) and the hydraulics got hot. My friend shut it down. About an hour later he cranked it for just a few seconds, it started & ran fine. We filled the hydraulic tank to proper level the next day.

Upon trying to start it would spin with black & gray smoke out the exhaust but would not start/run. The motor seemed to be spinning too slow/dragging & upon inspection we found the battery had several bad cells. There was also a good bit of sediment in the fuel bowl with no water apparent. We bought a new Die Hard battery (800 CCA manual calls for 750 CCA & old battery was 800 CCA) and new fuel filter. Also new battery terminals. I removed & cleaned the ground cable to frame & ground strap to block. Same thing, turned over with smoke but no start. I did purge the fuel system per the manual AND bled the injectors at the head to be sure (How much/strong should the fuel spurt out when injectors are cracked open at lines?)

The glow plugs appear good & tested 1.5 ohms resistance in each, removed. The fuel tank water drain yielded about a table spoon of water The fuel is fresh. The new battery was tested by 3 different places. NAPA, the local alt/starter re-builder and the place of purchase. All 3 said it's a good strong battery & NAPA also put it on the old style load tester & even with 50% charge (we had to charge it 2X after failed cranking attempts) the load meter barely moved.

I pulled the starter & took it to the re-builder. He pulled it apart & the armature was fair but had been hot. He's going to rebuild it with a new armature but he's on the fence as to whether that will solve the issue. I also have my doubts. While cranking the battery voltage drops from 13/12.5 down to 8 volts. Seems like a heavy draw? IDK.

We also tried with starting fluid, no difference. So, any ideas? I'm not a diesel mechanic, but am learning. I used to be an auto mechanic 30 years ago. I do know my friend ran the motor on the hot side about a month ago. The radiator was chock full of dirt/mud. He shut it down when he saw the temp indicator. Coolant is full/clean, no water in oil & no white smoke steam & he's been using it a lot since then. I don't think that's the issue.

Could it be fuel delivery? Weak pickup pump, injector pump issue? I'm at a loss. Sorry my first post is SOOO long but I really wanted to provide as much relevant info as possible to hopefully get some directional advice here. THANK YOU!

 

[Welder Dave]

NEVER use starting fluid on a Kubota. They have very tight clearances and can be destroyed in short order. Kubota's can a be a pain to prime but if you're getting smoke you're getting fuel. Did you try at full throttle? 8 volts cranking is drawing too much so a new starter turning it faster may solve your problem. Does the injection pump have a knob you turn out for priming that you close after it starts? It's not good to overheat a Kubota but if it ran fine after that isn't likely the problem. Not turning over fast enough could very well be the problem. My Kubota engine needs to turn fast to start.

 

[AGENT86]

Welder Dave, Got it on the starting fluid. I've rarely used it throughout my life anyway but my friend kept insisting & it is his machine so I finally relented. I did use it very sparingly, but no more. The priming knob is not present on this unit. It has a crimped non-movable cap where the knob is on other applications. Hopefully the rebuilt starter will resolve the issue. We did try full throttle position as well, no difference. I'll be installing he starter tomorrow. Fingers crossed!

Thank you for the reply & info, Welder Dave

 

[thepumpguysc]

How does the engine shut down.?? Key switch or cable.??
If its key, then the low voltage to the starter/draw could be interfering w the shut off solenoid.. not allowing it to fully retract..
IF its a 3 wire solenoid, it takes A LOT of amps to draw that sol. plunger IN..
If the reman starter doesnt solve the problem, find the shut off sol. & remove it to see if it starts..
Move that throttle to mid to full position while starting.. Good luck,

 

[AGENT86]

How does the engine shut down.?? Key switch or cable.??
If its key, then the low voltage to the starter/draw could be interfering w the shut off solenoid.. not allowing it to fully retract..
IF its a 3 wire solenoid, it takes A LOT of amps to draw that sol. plunger IN..
If the reman starter doesnt solve the problem, find the shut off sol. & remove it to see if it starts..
Move that throttle to mid to full position while starting.. Good luck,

It shuts off with the key. I installed the rebuilt starter today & same issue. It reminds me of an automotive engine with the timing too far advanced...if I had to describe it. I charged the battery prior to attempting to crank it. My digital charger states 90% capacity/FULL. I still feel that battery is not as good s the testers all say. My meter shows 12.5 volts after charging, the charger shows 13.6 but as soon as the charger shuts down that steadily drops down to 12.9/12.8 volts.

With the battery installed & my meter connected the voltage drops to 9.4 then below 9 into the 8.7 range. At that point I stop because I do not want to damage the starter. There is no way it's spinning near fast enough to start. I will check that solenoid tomorrow, hopefully that will be the answer. Thank you for your reply & info!

 

[Welder Dave]

Could there be aux. hyd's or something engaged causing it turn over slow and draw more power? I had accidently hit the aux. foot pedal in my skid steer getting out and it was hard to turn over.

 

[AGENT86]

Could there be aux. hyd's or something engaged causing it turn over slow and draw more power? I had accidently hit the aux. foot pedal in my skid steer getting out and it was hard to turn over.

After I checked the fuel shutoff solenoid today (it was 2 wire not 3 but I tried it unplugged anyway, no go) I checked for an aux like you posted. I couldn't find anything that would indicate that could be it. I do recall though, last week upon first attempt to crank after installing battery again the thumb snapped fully open moving a few inches (it wasn't closed but just shy of full open) when I turned the key to crank. That seemed odd. The boom has an internal seal going as it will slowly leak down when sitting or in use. Like I stated above, I'm not at all familiar with this machine & have a lot to learn this winter. Need to get it going asap now though.

This issue presented after he ran the hydraulic system hot. Perhaps your idea may still apply but in another scenario other than an aux control. I did try unplugging various connectors on the hydraulic system to no avail.

 

[Welder Dave]

That's a very important detail to leave out. Make sure the thumb valve isn't stuck partly open because that would cause slow cranking and higher power draw from the starter especially if running against the relief valve. If the hyd's got too hot may have damaged an O-ring or something and it's causing a problem in the thumb valve. Not sure if the thumb is electric controlled or direct from the valve but work the control back and forth and/or try closing the thumb while cranking. If direct linkage to valve just apply slight pressure to close thumb. If engine starts you found your problem. If you can get thumb to close some while cranking but still won't start, leave valve alone and see if thumb still opens when cranking. That would also tell you the problem is in the thumb valve. If the control is on the floor make sure the linkage and pedal are free and not binding or packed with dirt. What do you mean you unplugged various connectors on the hyd. system? If the thumb was disconnected but the valve was stuck would still try to pump fluid down the hose the same as any other aux. circuit.

 

[AGENT86]

That's a very important detail to leave out. Make sure the thumb valve isn't stuck partly open because that would cause slow cranking and higher power draw from the starter especially if running against the relief valve. If the hyd's got too hot may have damaged an O-ring or something and it's causing a problem in the thumb valve. Not sure if the thumb is electric controlled or direct from the valve but work the control back and forth and/or try closing the thumb while cranking. If direct linkage to valve just apply slight pressure to close thumb. If engine starts you found your problem. If you can get thumb to close some while cranking but still won't start, leave valve alone and see if thumb still opens when cranking. That would also tell you the problem is in the thumb valve. If the control is on the floor make sure the linkage and pedal are free and not binding or packed with dirt. What do you mean you unplugged various connectors on the hyd. system? If the thumb was disconnected but the valve was stuck would still try to pump fluid down the hose the same as any other aux. circuit.

I believe you may be on to something here. I'll check into the thumb valve in the morning. The thumb is controlled with a rocker switch on the joystick. The connectors I unplugged were all to do with the hydraulics. I unplugged four one at a time that were connected to valves and/or solenoids on the hydraulic tank. I would disconnect, attempt to crank motor & then reconnect. Nothing made any difference. I will try what you explained above, I'll post back at some point tomorrow. Thank you!

 

[Welder Dave]

A rocker switch may have nothing to do with a valve that won't center.

 

[AGENT86]

Without the service manual (on the way, gonna be a bit) I'm just tinkering. I did get it to turn over as fast as any engine, gas or diesel I've ever heard. The new battery & rebuilt starter are super. It should have started. It was blowing rich black smoke out the exhaust.

The thumb had bled down about half way closed. When I initially turned the key to crank it opened full at a moderate speed. While cranking I moved the manual lever that raises/lowers the blade. The blade went up & down lifting the machine as well. The motor would begin to spin fast at certain points in the up/down motion of the blade. If I moved the lever up/down without letting it reach full height or bottom, but back & forth while cranking the motor really spun strong & fast.

I suppose this confirms a hydraulic issue causing the drag on the motor & when i manipulated the lever it would release pressure allowing motor to spin. Still no start, though. Is there a sensor/switch that would prevent the motor from cranking if a hydraulic failure were present? My friend (actual owner of the machine) called me from SC today. He was at the place he purchased the thumb a few weeks ago. He spoke with the tech who told him nothing hydraulic would cause the motor to spin slow/drag or drain the voltage from the battery. he said the 90* fuel elbows were probably the issue, that they probably have water & sediment clogging them. I find this highly unlikely based on the way all the issues present & the info I've gotten here.

My neighbor down the road has limited (but more than me) knowledge/experience with diesel & hydraulics and he also agrees it's a hydraulic failure causing the problem. He also said relief valve issue although he was unable to identify exactly what/where to begin. He said "get the service manual!"

We may have to call someone in. I just haven't got the experience to root out the issue & not sure my friend wants to wait for the manual. I appreciate the advice/info from all who replied. I will update as things go & post the final outcome. I look forward to learning about these machines over the long cold winter that's just around that corner. Of course, any more info/advice/comments & help is more than welcome. THANK YOU ALL!

 

[Welder Dave]

Not sure if a service manual would diagnose the problem or not but if the thumb creeped down while sitting and then opened when you cranked it, you FOUND the problem! What does moving the blade have to do with anything if the thumb is causing the problem? Did you move the switch to close the thumb while cranking? The blade may have priority over the thumb and/or diverted most of the oil going to the thumb. The place that put the thumb on sounds clueless. I'm no hydraulics expert but anytime the pump is making a function move puts a load on the engine whether it's running or cranking. If it's running against a relief valve can use a lot of power. Thick black smoke, how long did you leave the glow plugs on? If the machine has a block heater plug it in for 2 or 3 hours to get the engine as warm as possible to try and start it and use the glow plugs for at least 30 seconds. If it starts and the thumb just wants to open, keep closing it and don't run the machine too long. You could do this long enough to get the machine on a trailer and take it to a repair shop. Maybe??? if something is stuck it will clear itself but best to have it checked out so it isn't a recurring problem.

 

[AGENT86]

Not sure if a service manual would diagnose the problem or not but if the thumb creeped down while sitting and then opened when you cranked it, you FOUND the problem! What does moving the blade have to do with anything if the thumb is causing the problem? Did you move the switch to close the thumb while cranking? The blade may have priority over the thumb and/or diverted most of the oil going to the thumb. The place that put the thumb on sounds clueless. I'm no hydraulics expert but anytime the pump is making a function move puts a load on the engine whether it's running or cranking. If it's running against a relief valve can use a lot of power. Thick black smoke, how long did you leave the glow plugs on? If the machine has a block heater plug it in for 2 or 3 hours to get the engine as warm as possible to try and start it and use the glow plugs for at least 30 seconds. If it starts and the thumb just wants to open, keep closing it and don't run the machine too long. You could do this long enough to get the machine on a trailer and take it to a repair shop. Maybe??? if something is stuck it will clear itself but best to have it checked out so it isn't a recurring problem.

The service manual would at least help guide me through the hydraulics, etc. I did try the switch but it doesn't function while cranking. I disconnected the quick-release fittings to the thumb lines & it cranked better but still too slow without manipulating the blade to release pressure. There is no block heater. The glow plugs are tied in with the key switch/start circuit so I can't operate them apart from that. They show as "ON" for about 10 seconds then the indicator shuts off which is when you can crank it. I do cycle the key for 30 seconds or more at times to see if that gets them hotter...IDK.

It will not start, just lots of black smoke with a touch of gray mixed in now. It's down in the woods so it would be great to at least get it running so we could bring it back up the hill & go from there.

 

[Welder Dave]

If the problem is the thumb valve, disconnecting the lines won't help because it will still try to pump fluid as explained previous. Try turning the key on for 10 seconds then turn the key off and turn it back on for 10 seconds a couple times. I think it will cycle for 10 seconds each time as long as you turn the key off between tries. I had a Hino truck like that, that took 3 or 4 cycles to start when it was below freezing. Have you checked the air filter?

 

[AGENT86]

If the problem is the thumb valve, disconnecting the lines won't help because it will still try to pump fluid as explained previous. Try turning the key on for 10 seconds then turn the key off and turn it back on for 10 seconds a couple times. I think it will cycle for 10 seconds each time as long as you turn the key off between tries. I had a Hino truck like that, that took 3 or 4 cycles to start when it was below freezing. Have you checked the air filter?

I've tried the 10 second on/off key/GP routine several times...no difference. Air filter is OK, have tried with AF removed as well. I'm going to remove the GP's again & instead of ohm testing will hotwire each plug to visually see if functional. This was recommended by the "tech" at the place the thumb was purchased. I don't think it's the GP's but may as well double check.
I shall report back with results later...thank you!

 

[steveme]

I've tried the 10 second on/off key/GP routine several times...no difference. Air filter is OK, have tried with AF removed as well. I'm going to remove the GP's again & instead of ohm testing will hotwire each plug to visually see if functional. This was recommended by the "tech" at the place the thumb was purchased. I don't think it's the GP's but may as well double check.
I shall report back with results later...thank you!

I know it’s been a while since you posted this but what was the end result of your problem? I’m basically in the same boat with a no start on the same Kubota.

 

[Welder Dave]

What symptoms do you have? Every engine is different so starting issues may not be the same. If it's turning over good and has black smoke you're getting fuel. First make sure none of the hyd. functions are activated. Try removing the fuel cap. If the vent is plugged it won't start or quit shortly after starting.

 

[steveme]

What symptoms do you have? Every engine is different so starting issues may not be the same. If it's turning over good and has black smoke you're getting fuel. First make sure none of the hyd. functions are activated. Try removing the fuel cap. If the vent is plugged it won't start or quit shortly after starting.

What symptoms do you have? Every engine is different so starting issues may not be the same. If it's turning over good and has black smoke you're getting fuel. First make sure none of the hyd. functions are activated. Try removing the fuel cap. If the vent is plugged it won't start or quit shortly after starting.

Cranks but doesn’t fire no smoke. Small amount of ether helped so I know it’s fuel related. I don’t believe hydraulics would have an effect of engine starting.

 

[Welder Dave]

A hyd. function activated would definitely cause a starting issue but no smoke is fuel related. Make sure the fuel shut mechanism is working. Has the fuel filter been changed recently? There could be a restriction in the fuel line somewhere. Maybe blow air through the inlet line. If filters and fuel lines are good could be the lift pump is bad. Could still try removing the fuel cap. Did starting get hard over time or all of a sudden? There's some more serious issues it could be but try the above first.

 

[steveme]

A hyd. function activated would definitely cause a starting issue but no smoke is fuel related. Make sure the fuel shut mechanism is working. Has the fuel filter been changed recently? There could be a restriction in the fuel line somewhere. Maybe blow air through the inlet line. If filters and fuel lines are good could be the lift pump is bad. Could still try removing the fuel cap. Did starting get hard over time or all of a sudden? There's some more serious issues it could be but try the above first.