M7040 will only start at full throttle, dies if you significantly reduce throttle

dolesorchard

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Kubota M7040, JD 5200, JD 790, JD 2030, JD 2440
Aug 5, 2022
6
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Maine
I recently bought a used M7040. A couple of weeks ago a stick kicked up while I was mowing and broke off the fuel transfer pump. It took forever to bleed the air out of the system, but I think that’s good now. At less than full throttle it will kick then die. When it’s running, if you very gradually reduce the throttle it will continue to run. If you cut the throttle at all abruptly, it dies. Any help will be greatly appreciated!
 

Tx Jim

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M7040 HDC-1,JD 4255,Ford 6700
Apr 30, 2013
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Coyote Flats,Texas
Have you attempted operating engine with a shop towel covering fuel tank neck in lieu of fuel cap IE is tank vent open?
 

JerryMT

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Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
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The Palouse - North Idaho
I recently bought a used M7040. A couple of weeks ago a stick kicked up while I was mowing and broke off the fuel transfer pump. It took forever to bleed the air out of the system, but I think that’s good now. At less than full throttle it will kick then die. When it’s running, if you very gradually reduce the throttle it will continue to run. If you cut the throttle at all abruptly, it dies. Any help will be greatly appreciated!
Did you replace the lift pump? It's usually needed to supply fuel at 4-5 psig to the injector pump.
 

dolesorchard

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Equipment
Kubota M7040, JD 5200, JD 790, JD 2030, JD 2440
Aug 5, 2022
6
0
1
Maine
Have you attempted operating engine with a shop towel covering fuel tank neck in lieu of fuel cap IE is tank vent open?
I haven’t, but will try it. It was running perfectly before the fuel pump got broken off.
 

PoTreeBoy

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L35 Ford 3930
Mar 24, 2020
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WestTn/NoMs
I was going to mention 2 things
* pull the fuel line off at the injector pump and see if you get a good stream of fuel when you crank it over. If the original pump physically broke, there could be internal damage
* maybe the stick also physically damaged the governor/throttle linkage?
 

dolesorchard

New member

Equipment
Kubota M7040, JD 5200, JD 790, JD 2030, JD 2440
Aug 5, 2022
6
0
1
Maine
I was going to mention 2 things
* pull the fuel line off at the injector pump and see if you get a good stream of fuel when you crank it over. If the original pump physically broke, there could be internal damage
* maybe the stick also physically damaged the governor/throttle linkage?
The governor is something I was thinking about, it seems like when I try to start it at less than full throttle it starts to run fairly high, then the governor kicks in and it dies. Can you tell m more about it?
 

PoTreeBoy

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L35 Ford 3930
Mar 24, 2020
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WestTn/NoMs
The governor is something I was thinking about, it seems like when I try to start it at less than full throttle it starts to run fairly high, then the governor kicks in and it dies. Can you tell m more about it?
Sorry, no help. I understand lawn mower governors, but haven't studied diesels.
 

lugbolt

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ZG127S-54
Oct 15, 2015
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Mid, South, USA
Generally if there is air or even a restriction in the fuel system somewhere it'll do just the exact opposite...once the engine is placed under load (i.e., full throttle), it would begin to bog and possibly die from lack of fuel, or more specifically insufficient volume to support the engine load.

Your description sounds more like a possible injection pump issue, or perhaps a governor issue.

Maybe a fuel shutoff issue-that's pretty common on some of the older RTV's and mowers where the shutoff solenoid is on top of the engine; the solenoid (or lever) would stick and then cause hard starting unless you advance the throttle. Then as you'd let the lever back to "idle", the engine would die. Did lots of them. BX's too. With that said you might check your injection pump and see if it has a manual shutoff lever on it. If it does, is it partially off? Maybe a stick jammed in there or something? Move the lever by hand back and forth, should have a positive stop in both directions.
 
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PoTreeBoy

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L35 Ford 3930
Mar 24, 2020
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WestTn/NoMs
Screenshot_20220805-194157-678.png

Here's the stop lever assy lugbolt mentioned. Maybe something got bent or that torsion return spring is fouled up.