# JD 790 Spring start up problems...



## JKWill (Mar 21, 2014)

Hey guys...first post.

JD 790 (13-14 year old-600 hours). Do all normal maintenance. Ran my fuel tank dry 12-15months ago. Filled with good fresh fuel and installed new battery . Fired right up, but throttle control had no effect on RPMs, which went to max (2500ish) and stayed there despite throttle position for about 15 seconds, then slowly and steadily decreased until it just shut off. Pulled side cover, cleaned and lubricated linkage, Fuel filter had little use and looked good, but I replaced it anyway and cleaned (barely dirty) air filter.

The dash lights come on normally, and the starter cranks likes it's brand new. But it will not fire. Not a lick.

I cycled all the levers and switches several times, checked the one under the seat (positionally, not electrically).

Any ideas? Poor as a church mouse and had a little cutting job would have provided a couple of desperately needed Benjimens. 

Bought the battery and downloaded a repair manual with that in mind, but now I'm just stuck and she is mad and cancelled job...sigh. City folks.

Still need a working tractor out here Could really use some help.

JW


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## Hoodoo Valley (Nov 14, 2006)

No advice to give you but welcome to the forum!


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## 82corvette (Jul 8, 2011)

Gently tap the carburetor bowl. Sometimes the needle and seat stick & won't let fuel thru. I always run Stabil & keep the fuel tank full so it doesn't get condensation.


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## Hoodoo Valley (Nov 14, 2006)

82corvette said:


> Gently tap the carburetor bowl. Sometimes the needle and seat stick & won't let fuel thru. I always run Stabil & keep the fuel tank full so it doesn't get condensation.


82Corvette I 'm fairly certain this is a diesel powerplant.


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## JKWill (Mar 21, 2014)

Yup...diesel fuel. No carb.


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## Thomas (Nov 1, 2006)

Does the 790 have glow plugs?


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## Halifax (Oct 8, 2009)

I don't have a JD, but the injector pump on my tractor gets the oil changed out every time I change the engine oil. Not sure but it sounds like the governor went WOT due to lack of lubrication or gummed up inside. I do not know what maintenance JD allows the owner to perform. I have drain and fill bolts to determine the correct level.

Side note, the injector pump takes a pro to disassemble, adjust. Changing the oil and maybe adjust the cables is all the typical owner would do.

Good luck

Aubrey


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## Hoodoo Valley (Nov 14, 2006)

Thomas said:


> Does the 790 have glow plugs?


They don't Thomas. They have an air intake heater.


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## Thomas (Nov 1, 2006)

Thanks TB.


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## JKWill (Mar 21, 2014)

Halifax:

Changing the oil inside the injector pump is not a maintenance item recommended by JD. But I agree with you about the governor and it's behavior. After cleaning and lubricating all of it that I can with disassembling it, it feels loose and functional now. 
I'm hip about the injector pump. I'm a retired electromechanic, but it is beyond my abilities and tools to work on.

At this point, after looking at two manuals and the included one line diagrams and schematics, I believe it's an electrical problem at this point. Although initially the governor was a big issue. Since fuel will not travel up to the motor (no smoke when I crank it).

I'm suspecting the circuit that involves the fuel cutoff solenoid. The are 4 or 5 electrical operations that have to happen, or that sucker just remains closed, cutting of the fuel to the engine.

Not being a John Deere/Yanmar guy, those are just suspicions though. Going to pull off the panel and go through and check the components involved in getting fuel into the motor.

Going to be a pain, as I'm retired because of my disability. But I don't have $100 per hour (plus parts) to pay for the local shop in Athens to shotgun troubleshoot my tractor.

And TractorBeam, you seem to know more about my machine than I do. Wish you lived next door. 

Still very open to ideas...at best this is going to take me weeks to eliminate components that are functioning correctly. Not even going to consider the injector pump, as that will mean parking it indefinitely and buying some beat up Kubota at a later date.


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