M120 fuel starvation

cwaltz21

New member

Equipment
M120, M9000
Apr 23, 2024
6
0
1
PA
I have an early 2000s m120 that started giving me fits last year. 2700 hours.

Machine will bog down, go down to 100-200 rpm, and either spit sputter and puff black smoke and then come back to life, or die out. Does it under a load or without, however it seems to happen more after it's been put under load. Changed the fuel filters, didn't help. Pulled the separator apart, didn't see anything, and put it back together till the new seals came in. At that point we were using it only to haul the round bale wagon and it stopped giving us problems, so I held off on the separator seals.

Changed filters and did the separator seals this spring, and fought to get machine primed. The manual prime just acted like it wasn't building pressure. At one point it did, then I tried to start the tractor, no luck, and the manual prime stopped building pressure again. However...diesel seems to push it's way up out of the primer.

Went to disc today in super nice loose soil and it started acting up again. Wasn't so bad at first, generally just thought I got in a soft spot, but then it got progressively worse. Sputter discing up hill, sputtered discing down hill, right side of the tractor on the high side, left side of the tractor on the high side, did it when I had the disc's up and just turning on the headland, and in low or high range.

I've seen this talked about, but never any answers given...could the seal in the manual prime pump be sucking air? Can it do this even when it's down and screwed shut? Is there a screen somewhere in the separator I missed? Fuel lines deteriorated? Someone mentioned a diaphragm in the lift pump? Or the smaller m8xxx series having a relief valve that needs opened before you prime?Any bit of help will be appreciated, I plan on using this tractor a lot more this year.
 

Fedup

Active member
Apr 6, 2016
264
85
28
Winchester
I would offer this simple suggestion, It's a trick I have used more times than I can count. Take an electric fuel pump, (typical parts house universal type) and tie it on somewhere near the fuel filter. Remove the fuel supply hose from the first filter and fit it onto the pump inlet. Add a hose from pump outlet to the filter base. Hook up whatever it takes to get 12 volts to power the pump. Any temporary jumper wire type of thing straight to battery will work. Now bleed out the fuel system. You might be surprised at how quickly it goes as compared to where you are now. Then start and run the tractor for a while. Maybe take it out and work it a bit and see what happens. If you like what you see you might consider mounting the pump permanently and wiring into the fuel shut off circuit. I have no idea how many times I've done just that. I keep a pump or two on the shelf all the time.
 

cwaltz21

New member

Equipment
M120, M9000
Apr 23, 2024
6
0
1
PA
I would offer this simple suggestion, It's a trick I have used more times than I can count. Take an electric fuel pump, (typical parts house universal type) and tie it on somewhere near the fuel filter. Remove the fuel supply hose from the first filter and fit it onto the pump inlet. Add a hose from pump outlet to the filter base. Hook up whatever it takes to get 12 volts to power the pump. Any temporary jumper wire type of thing straight to battery will work. Now bleed out the fuel system. You might be surprised at how quickly it goes as compared to where you are now. Then start and run the tractor for a while. Maybe take it out and work it a bit and see what happens. If you like what you see you might consider mounting the pump permanently and wiring into the fuel shut off circuit. I have no idea how many times I've done just that. I keep a pump or two on the shelf all the time.
I'm assuming that's enough to overcome any air it could possibly be pulling?

I'm more of a fix the root problem than find a work around type guy. Too many years of fixing redneck engineering of generations past.
 

Tx Jim

Well-known member
Lifetime Member

Equipment
M7040 HDC & JD 4255
Apr 30, 2013
1,218
139
63
Coyote Flats,Texas
Is fuel tank venting? I once owned a M4900 that acted similar to your M120. Local Kubota service manager advised me to check for restriction in water separator gallies. I remove fuel control valve from water separator housing & I located a tiny screen that was clogged. Cleaned the screen, reassembled & engine operating problem was solved