L2501 Modifications

NetMagi

Member

Equipment
BX25D (sold), L2501HST w/BH77 Backhoe
Dec 30, 2014
99
23
8
Pennsylvania
I bumped my throttle-limit up to 2750rpm this last weekend, as measured by an optical RPM gauge. The gauge on the dash was pretty darn close.

Based on the dyno sheet from the 1703 as 'timed' for the L2501, I didn't expect much difference, but wow, big difference from my perspective. I generally only run ~1800-1900 RPM's, but when I needed the power, I was running it wide open before and it still just seemed a little light on grunt. Now if I want the power, if I set the no load rpm's around 2550-2600, under load it pulls down to ~2450 and feels A LOT stronger. The 'M' gear on the HST becomes much more usable for travel as well. I expected H to become useless at WOT, given the rpm increase also driving up the ground speed, but dang if this thing does get up to ~15mph faster than it got up to ~12mph before.

I know folks are really divided on any mods like this, and if I was running this thing WOT on a construction site all day I'd probably expect a small reduction in usable lifespan, but I'm a homeowner and this thing will probably long outlast me, even if I set the revs to 3k, turbo'd it, and bumped timing past spec.

If you're reading this years later, and want to know it it 'blew up', feel free to ask me :)

The only 3-pt implement I run is a 64" snowblower. I look forward to trying it with a little more revs next winter. Yeh, I'll be over the rated PTO speed, but the SB1064 seems to turn slower then the mid-mount PTO driven blower I had on the front of my BX anyway. My guess is if I set no-load ~2500 and let it pull down to ~2300 by modulating my speed into the snow it'll probably do great.

If you want to try this yourself, it's this easy:

1. open hood
2. remove the black plastic cover that sits just under hood level on the loader-valve side of the tractor (3 bolts)
3. move the throttle control from the dash and watch which bolt the linkage stops on when set to wide-open throttle.
4. once you identify the right bolt, unwind and remove the safety wire from the bolt head. you don't need to cut it, it's just wrapped around
5. loosen the stop-nut and back the bolt out a half inch or so.
6. start the tractor and SLOWLY increase the RPM's with the throttle until you reach the desired RPM you want it to stop at. If it still doesn't get as high as you want, it may still be hitting the bolt. Just back it out a little further. Remember the dash gauge doesn't show actual RPM's immediately. You want to raise the throttle very slowly to avoid over-revving.
7. once at the desired high-rpm (I wouldn't go above 2800), slowly turn the bolt back in until it contacts the throttle linkage, and tighten the stop-nut.
8. back off the throttle and then go back to WOT, and re-confirm the bolt is stopping it at the rpm you want before buttoning it all back up. I re-installed my safety wire, just for completeness.
9. enjoy the extra power

A word of caution: This bolt is painted *after* being set by Kubota at the factory. After adjusting it, you can clearly see that it's been adjusted. If you're under warranty, I wouldn't give Kubota any reason to deny a claim. Just wait till the warranty is out.
 
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Luckyman84

New member

Equipment
L2501 DT
Apr 1, 2021
4
5
3
Virginia
Now that is how you do an easy to follow write up my man. Thank you. My L2501 is far from out of warranty, so this mod will have to wait.
 
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Reactions: 1 user

NetMagi

Member

Equipment
BX25D (sold), L2501HST w/BH77 Backhoe
Dec 30, 2014
99
23
8
Pennsylvania
FYI, for anyone who wants to nerd out on it, if you just bump up the revs like I did, extrapolating out from the published dyno's, you're a bit over 28hp, or ~15% increase. If you were to bump ignition timing to 10deg BTDC, you'd unlock over 36hp (based on Kubota's published #'s for D1703-M-DI's timed @ 10deg)

I will tell you, my butt dyno tells me it feels like more than 15%, but I think it's because the stock limit drags it down so far under any real load.

If I get bored enough one day, I'll prolly pull it into the shop and bring my timing to ~7 degrees. That should be good for ~30hp @ 2800rpm's. Unfortunately, that looks like actual work vs. adjusting the rpm limit bolt, which took 5 mins :)
 
Last edited:

tractorX

New member

Equipment
KUBOTA L2501 DT 4WD 525 FEL SSQA, 5' BOX BLADE, 42" FORKS, PIRANHA TOOTH BAR
Sep 27, 2013
17
8
3
Rock Spring GA.
FYI, for anyone who wants to nerd out on it, if you just bump up the revs like I did, extrapolating out from the published dyno's, you're a bit over 28hp, or ~15% increase. If you were to bump ignition timing to 10deg BTDC, you'd unlock over 36hp (based on Kubota's published #'s for D1703-M-DI's timed @ 10deg)

I will tell you, my butt dyno tells me it feels like more than 15%, but I think it's because the stock limit drags it down so far under any real load.

If I get bored enough one day, I'll prolly pull it into the shop and bring my timing to ~7 degrees. That should be good for ~30hp @ 2800rpm's. Unfortunately, that looks like actual work vs. adjusting the rpm limit bolt, which took 5 mins :)
"started off doing a basic rpm increase to 2600rpms. It helped with running my PTO chipper but I eventually found out I needed more fuel. I made a very slight fuel adjustment and it did increase the power. Only issue was of course slightly more smoke. After reading about the D1703 I figured out Kubota retarded the timing to 5 degrees btdc for emissions and to help it get under 25hp and also the air box they are using is a major restriction. The 1703 can run up to 14 degrees btdc. I bumped the timing up to 9 btdc and installed a higher flowing air box and all I can say is wow this thing pulls up my driveway which is a 15% grade like no problem in mid range gear at 2300rpms."
OP

@NetMagi, ive tried reaching out, guess the OP has bounced or doesn't have time.
can you help me with timing, direct injectors and air. i talked to a diesel mechanic that said he could do this no problem... but like to see if this is something i could do.
appreciate the help.
 

NetMagi

Member

Equipment
BX25D (sold), L2501HST w/BH77 Backhoe
Dec 30, 2014
99
23
8
Pennsylvania
"started off doing a basic rpm increase to 2600rpms. It helped with running my PTO chipper but I eventually found out I needed more fuel. I made a very slight fuel adjustment and it did increase the power. Only issue was of course slightly more smoke. After reading about the D1703 I figured out Kubota retarded the timing to 5 degrees btdc for emissions and to help it get under 25hp and also the air box they are using is a major restriction. The 1703 can run up to 14 degrees btdc. I bumped the timing up to 9 btdc and installed a higher flowing air box and all I can say is wow this thing pulls up my driveway which is a 15% grade like no problem in mid range gear at 2300rpms."
OP

@NetMagi, ive tried reaching out, guess the OP has bounced or doesn't have time.
can you help me with timing, direct injectors and air. i talked to a diesel mechanic that said he could do this no problem... but like to see if this is something i could do.
appreciate the help.
The procedure for injector timing is covered in the workshop manual for the L2501, page 1-S15 (pg 103 of the pdf)

I would post it here, but not sure if that is permitted

It's on kubotabooks, so I'm assuming it's ok to post it here. If not, please advise and I will remove it:

 
Last edited:

tractorX

New member

Equipment
KUBOTA L2501 DT 4WD 525 FEL SSQA, 5' BOX BLADE, 42" FORKS, PIRANHA TOOTH BAR
Sep 27, 2013
17
8
3
Rock Spring GA.
The procedure for injector timing is covered in the workshop manual for the L2501, page 1-S15 (pg 103 of the pdf)

I would post it here, but not sure if that is permitted
thank you ill look it up. keep me post after you advance the timing. are you gonna adjust the fuel... any ideas on bigger air box?
 

NetMagi

Member

Equipment
BX25D (sold), L2501HST w/BH77 Backhoe
Dec 30, 2014
99
23
8
Pennsylvania
thank you ill look it up. keep me post after you advance the timing. are you gonna adjust the fuel... any ideas on bigger air box?
I'm guessing that bigger airbox isn't needed unless you turbo, but I would defer to OP. He also states that up to 14 BTDC timing is ok, but be advised that based on my research anything over 11 degrees is out of spec per kubota for the DI variant of the 1703.

I updated my prior post to include the URL for the WSM
 

NetMagi

Member

Equipment
BX25D (sold), L2501HST w/BH77 Backhoe
Dec 30, 2014
99
23
8
Pennsylvania
I'm guessing that bigger airbox isn't needed unless you turbo, but I would defer to OP. He also states that up to 14 BTDC timing is ok, but be advised that based on my research anything over 11 degrees is out of spec per kubota for the DI variant of the 1703.

I updated my prior post to include the URL for the WSM
Worth noting that a lot of previous posts comparing the engine in the L2501 were looking at older indirect injection variants of the 1703. Many have argued that the engine in the L2501 is unique and has different parts. That's true if comparing to the much older indirect injection 1703's and MIGHT be true in the 1703 in the L2501 as well, but I don't buy it. If you're Kubota and you can either:

a) take an existing engine, change zero parts, but set max RPM to ~2400 and retard timing to stay safely under the emissions HP limit

or. . .

b) make a whole bunch of unique custom parts for an engine that you ship in one tractor

I mean c'mon. . :p

We already know that the timing is ~4 BTDC vs ~10 BTDC and it's rev-limited .. . so why do that AND change parts. It makes zero sense from a business perspective. If someone is still unsure and wants to really chase this one down to ground, you could always compare the parts trees between the 1703's and look at part #'s to confirm.
 
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tractorX

New member

Equipment
KUBOTA L2501 DT 4WD 525 FEL SSQA, 5' BOX BLADE, 42" FORKS, PIRANHA TOOTH BAR
Sep 27, 2013
17
8
3
Rock Spring GA.
I'm guessing that bigger airbox isn't needed unless you turbo, but I would defer to OP. He also states that up to 14 BTDC timing is ok, but be advised that based on my research anything over 11 degrees is out of spec per kubota for the DI variant of the 1703.

I updated my prior post to include the URL for the WSM
found the WSM. yeah i think ill stick with 7-9 range on the timing to be on the safe side. thanks again for the help!
 

72401L2501

New member

Equipment
L2501
May 3, 2021
4
1
3
Jonesboro, AR
Excellent information! I'm new here and actually made an account just because of the L2501 turbo/engine mod thread. Any videos after injector timing or of it working now?
 
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Reactions: 1 user

802Driver

Active member

Equipment
LX2610SU 60" Bucket Land Pride54" Box Blade Farm King 4572 Rear Blade
May 18, 2020
107
65
28
Manitoba, Canada
No problem I will make a guide on the changes I made and the power expected.

Also major update!!!!!
I just finished installed a MHI tdo3 7G turbo. This is the same setup on the v2003t Kubota engine. It spools beautifully and this tractor is making at least double the hp. It literally flies up my hill in H gear. The sound is absolutely amazing and this turbo cleans up very nice no smoke the tractor runs super clean under a load. if you anyone is interested let me know. I’ll ship you a kit 😎🤘 here are some teaser photos. The exhaust is not done and the adapters I made still need some trimming and I will be ceramic coating all 304ss hot parts. Check it out!!
Hahaha, that's awesome(y)(y)
 

Mikemoto17

Member

Equipment
L2501 HST BH77 backhoe LA525 loader woodland Mills Pto chipper
Oct 21, 2020
10
35
13
California
Hey Guys! I am still here. To be honest I like to test everything I make so that’s what I’ve been doing. Let’s just say it has now had over 100hrs of brutal testing with my turbo setup running 10-12 psi boost and no issues at all. I ended up bumping my hydraulic pressure up 500psi as well since I needed more rock breaking power with the bh77. I finally found someone with a PTO dyno. Once I get an idea of what it’s making I’ll let you guys know on offering it for sale soon!!

I just got done building a 2,000sqft fabrication shop. I’ve been slammed!!!!! Sorry for the delays and not responding. If you have any questions let me know!
 

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Rdrcr

New member

Equipment
L2501, B2601
May 7, 2021
5
0
1
WA
"started off doing a basic rpm increase to 2600rpms. It helped with running my PTO chipper but I eventually found out I needed more fuel. I made a very slight fuel adjustment and it did increase the power. Only issue was of course slightly more smoke. After reading about the D1703 I figured out Kubota retarded the timing to 5 degrees btdc for emissions and to help it get under 25hp and also the air box they are using is a major restriction. The 1703 can run up to 14 degrees btdc. I bumped the timing up to 9 btdc and installed a higher flowing air box and all I can say is wow this thing pulls up my driveway which is a 15% grade like no problem in mid range gear at 2300rpms."
OP

@NetMagi, ive tried reaching out, guess the OP has bounced or doesn't have time.
can you help me with timing, direct injectors and air. i talked to a diesel mechanic that said he could do this no problem... but like to see if this is something i could do.
appreciate the help.
Edit....didn’t even see that the OP posted, lol!!!
Welcome back!!!

I’ve spoken to the OP, he’s busy and hasn’t had an opportunity to get back on the forums to post an update.

His tractor is still running strong with the turbo and 2,600 RPM rev limit. He now has over 100 hours on the setup.

Mike
 

Rdrcr

New member

Equipment
L2501, B2601
May 7, 2021
5
0
1
WA
I bumped my throttle-limit up to 2750rpm this last weekend, as measured by an optical RPM gauge. The gauge on the dash was pretty darn close.

Based on the dyno sheet from the 1703 as 'timed' for the L2501, I didn't expect much difference, but wow, big difference from my perspective. I generally only run ~1800-1900 RPM's, but when I needed the power, I was running it wide open before and it still just seemed a little light on grunt. Now if I want the power, if I set the no load rpm's around 2550-2600, under load it pulls down to ~2450 and feels A LOT stronger. The 'M' gear on the HST becomes much more usable for travel as well. I expected H to become useless at WOT, given the rpm increase also driving up the ground speed, but dang if this thing does get up to ~15mph faster than it got up to ~12mph before.

I know folks are really divided on any mods like this, and if I was running this thing WOT on a construction site all day I'd probably expect a small reduction in usable lifespan, but I'm a homeowner and this thing will probably long outlast me, even if I set the revs to 3k, turbo'd it, and bumped timing past spec.

If you're reading this years later, and want to know it it 'blew up', feel free to ask me :)

The only 3-pt implement I run is a 64" snowblower. I look forward to trying it with a little more revs next winter. Yeh, I'll be over the rated PTO speed, but the SB1064 seems to turn slower then the mid-mount PTO driven blower I had on the front of my BX anyway. My guess is if I set no-load ~2500 and let it pull down to ~2300 by modulating my speed into the snow it'll probably do great.

If you want to try this yourself, it's this easy:

1. open hood
2. remove the black plastic cover that sits just under hood level on the loader-valve side of the tractor (3 bolts)
3. move the throttle control from the dash and watch which bolt the linkage stops on when set to wide-open throttle.
4. once you identify the right bolt, unwind and remove the safety wire from the bolt head. you don't need to cut it, it's just wrapped around
5. loosen the stop-nut and back the bolt out a half inch or so.
6. start the tractor and SLOWLY increase the RPM's with the throttle until you reach the desired RPM you want it to stop at. If it still doesn't get as high as you want, it may still be hitting the bolt. Just back it out a little further. Remember the dash gauge doesn't show actual RPM's immediately. You want to raise the throttle very slowly to avoid over-revving.
7. once at the desired high-rpm (I wouldn't go above 2800), slowly turn the bolt back in until it contacts the throttle linkage, and tighten the stop-nut.
8. back off the throttle and then go back to WOT, and re-confirm the bolt is stopping it at the rpm you want before buttoning it all back up. I re-installed my safety wire, just for completeness.
9. enjoy the extra power

A word of caution: This bolt is painted *after* being set by Kubota at the factory. After adjusting it, you can clearly see that it's been adjusted. If you're under warranty, I wouldn't give Kubota any reason to deny a claim. Just wait till the warranty is out.
Great tutorial!

Thanks for posting!

Mike