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My first instinct is that it may be a blocked vent in the fuel cap. The next time it starts to loose RPM, remove the fuel cap before it dies. If it recovers, there is your problem. If it goes ahead and dies, it is something else.
Next best guess is a plugged fuel filter. Easy and cheap to replace. Probably wouldn’t hurt anyway as they tend to get ignored. If that is the problem, you really want to open that filter and see what is plugging it. It could be the dreaded diesel bugs. In that case you need to take care of it as quickly as possible to prevent more damage. Bob Rooks has posted a lot about the bugs and how to clean up after an infestation. I sure hope that is not it.
Other things of lower probability are governor problems (an oil change there is always a good idea), air in the system, vapor lock (fuel line overheating?), and probably several others that I haven’t thought of.
Good luck and let us know what you find.
On my tractor, if I am working on a pile (nose high, tail low) and my fluid level is low, the system will suck air and I first notice it by the FEL either not going all the way up or jerking and bouncing as the air makes its way through the system.
I am not familiar with your exact tractor so the following is based off of my Jinma 284 which should be similar.
The hydraulic tank is under the seat with a fill plug behind the seat. The 3-point cylinder is inside the tank. There is a filter inside the tank (strainer really) that screens the oil as it is sucked out on its way to the pump.
Fluid from the pump goes to a hose with a quick coupler. If the FEL is installed the fluid goes through the loader valve then exits and connects to the tractor through another coupler.
From there it goes to the 3-point valve and eventually dumps back into the tank. (Mine is different in that it only has one pump and uses a priority valve to power the steering).
If the quick coupler were a problem it would likely dead-head the pump and probably destroy it, at least blow a hose off. It wouldn’t recover from that after a cool down.
One quick and easy test is to put some weight on the 3-pt. and run it until the FEL stops working. Put the bucket and 3 point down, turn off the engine. Then disconnect the couplers and plug the tractor side lines into each other, thus taking the FEL out of the circuit. Start the tractor and see if the 3 point will raise. If it works the problem is in the FEL. I suspect it won’t work, but at least we will have eliminated a possibility.
Next, take out the fill plug and suck some fluid up with something. Suck gun, large syringe, turkey baster, anything that will allow you to get a sample into a transparent container. If the fluid is milky or hazy looking it may have air in it. Let it sit for an hour or two and see if it clears up. If there is air in the fluid you probably have a suction side leak somewhere. Post a picture if you can.
One question about this. Just before the hydraulics quit, do you notice any difference in the operation of the FEL? Slow to respond or jerkiness?
Do you have a manual for this tractor? I am curious as to where the pressure relief valve is located?
At this point since your problem only shows up “hot” I am leaning more towards a problem with the fluid as a mechanical failure is less likely to start working again.
A couple of things come to mind.
The fluid viscosity is too low
There is air in the system
If the viscosity goes down (when hot) to the point that it can not “push” you loose efficiency to the point that it appears to stop working.
If your fluid is getting air drawn into it the results will be the same, loss of viscosity.
In both cases either cooling down or allowing the air to rise out of the mix will restore functionality.
Have you checked the fluid for level, cleanliness, air (or water) entrainment?
What is the temperature of the fluid when it stops working? You should be able to touch the loader control valve without being burned.
Do you know the type of fluid that is currently in the tractor?
I suspect the 3 Point mower has taken over do to the “universal” fit. Smaller compact tractors from the big manufacturers all have proprietary belly mowers with unique attachments and PTO setups.
I don’t believe I have ever seen a belly mower on a Jinma or clone.
The fuel cut off lever should be full forward to be in “Run”.
The throttle linkage is at idle when full forward. See Picture.
If your throttle linkage is not loose and you had a run away, I suspect there is an issue with the governor. I would recommend draining and replacing the oil as the first easy step. Instructions are on page 40 of this document:
http://harnerfarm.net/Jinma/Files/jinma_manual.pdf
Thanks Bob,
Any word on why the site was down?
You can get me at Stuart@harnerfarm.net in case it goes down again.
What tractor do you have?
It would appear that there is a breather on the end of that steel line. It also appears that the steel line is a return to the tank. The question is what tank?
I would highly suspect a blown seal on the backhoe pump as the backhoe has a separate hydraulic system and that fluid should never be introduced to the tractor side of things.
Hmm. I would have to see specs and instructions to give sound electronics advice.
If your new gauge requires more resistance than provided by the factory sending unit, it should be a simple task to add the appropriate sized resistor in the line from the gauge to the sender.
Can you provide a schematic or instructions for the new gauge?
