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The Shop
Running the jetting specs on page 1, with the exception of 60:1, 1.5 gallons 93 pump with 0.5 gallons of VPR and Motorex cross power 2T oil
Bike has been running awesome, until yesterday….
About 800 ft elevation, central IL
Bike has a ProCircuit pipe, ProCircuit 304 silencer, VForce V4 reeds, vented airbox cover
Just did a top end at 58 hours, ran a few local races & practices, then a regional, then our motos at the ranch, the bike has not been babied, we are at 73 hours and ran into a overheating issue yesterday, pulled the top end and found signs of detonation on the head. Big score on the exhaust side of the piston next as shown.
Question is, are we jetted too lean or is it the mix 55:1 vs 60:1 an issue (I would think 55:1 would be more prone to detonation from a lean condition)
My first thought is you developed an air leak. Jetting doesn't change itself and suddenly "go bad" and unless environmental conditions had a drastic change that would explain it, it's likely an air leak. Being summer time, if anything the bike should be getting richer from the weather, not leaner.
The carbon pattern makes me think you developed this lean condition (likely air leak) rather recently and suddenly. It looks like there's the original carbon with some piston washing around the edges, like you'd want to see.. and then the clean edges started also getting carboned recently from the newfound heat.
Another thought... that wrist pin got really hot. I'd either swap pistons and pins more often and/or drill some oiling holes in the pin bores in the piston.
Mods: gizmo mods reed block
Fmf shorty that came with the bike
PJ: 32.5
Needle 42-74 pos 2
Needle jet: s7
Slide 5.0
Mj: 490
Amsoil dominator 32:1 Sunoco leaded 110/rec90 50/50
The track I was at is fast, and deep sugar sand. I’m at sea level in Florida temp was about 95*. I run B class towards the front in harescrambles, local moto, and the bike was wfo most of the time. I’m trying to avoid this again lol. Do I go straight to a 540mj and go from there? The bike never once hinted it was lean, and pulled clean from bottom to the top with zero bog. I prefer to stay with 32:1. The piston and rings looked great to be honest, rings were free as can be. Bike will be back together by the weekend, as I got the crank back today. Just looking for opinions so this doesn’t happen again lol.
That said, a few pages back there is some other 125 jetting that others have had luck with. You can put a 540 main jet in, but as digger has pointed out before that the carb isn’t capable of flowing that so it doesn’t matter if it’s in there or not that small bore is only able to pull so much fuel. One of these days I’ll go back and find it and update the first page.
You definitely will want to be in the 510-540 range on the main going WFO in sand at sea level. As AJ said, Digger will tell you that after 510 or so going bigger doesn't much help since the needle-jet or carb orifice itself becomes the limiting factor. But I will tell you I can definitely feel a difference from 510-520, 520-540.. and even a little bit 540-560.
Don't be afraid to try going a little richer on the needle also. Basically experiment so you know what's what. When the temps or elevation drop, I will run a 43-74 on (2) or even the 42-74 on (3).
The thing is all these settings are with an S4 which is slightly leaner than the S7. Combining these pilot or main suggestions with the S7 might make it too rich.
I do not thinks it’s a jetting related issue. I think it’s simply a manufacturing issue. They are all still using oem cranks. One of the 125’s is using a Keihin setup and the others are still on the setup Mikunis , similar to yours.
Done with heat cycles I’ll be doing plug chops this time. Do you guys think it’s necessary to bump to 40:1?
I’m aware of the big end bearing issue on the newer ktm’s. The guy that does my cranks also does them for a local shop that does a lot of mod bikes aswell. They noticed the 22+ had a metallurgy problem with the rods as both were getting trashed. They would install a pro-x before ktm knew they had a rod problem and the bike would be fine afterwards. Another local guy was having issues with other brands doing the same, he kept losing the big end bearing with motorex at 32:1. This guy is an ex factory Honda mech for the amatuer team. He had switched to a castor based oil and never had a problem since. Don’t know if any of it has any resonance or if it was all just a coincidence as it ranged from an 85 to a few 125’s also in about a 10 hour span.
Again, thank you guys for the response and help.
For the 125, Slide #5 is what you want. They do go out of stock at JD Jetting but come back in stock regularly.
Slide 5 https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-sli…
Jet Block gasket https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/
S4 Needle Jet KTM PN 55431021400
YZ125 6BFY 42-74 needle Yamaha PN 284-14116-H4-00
Mans & pilots, buy OEM Yamaha or KTM, whichever is cheaper.
Pit Row
I always like to experiment so I know what is what. If the 500 main feels good. go to a 510.. and then a 520.. keep going richer until you find the point of too much.. then back it off to the sweet spot. Same for the needle clip. Clip-2 might be good at the higher tracks but clip-3 might be better at Washougal. Only one way to really know.
I routinely run 37.5 pilot, clip-3 and big mains like 540-560 when the temps drop, but I am running AvGas which leans everything out.
Oh, I don't know if extra oil will help the 2022 crank probs. but 40:1 is plenty with Super-M under normal circumstances, at least me flogging my 2021 tells me so.. lol
I actually did notice some ongoing plating wear in my 5.5 slide so for next seasong im going to either file/machine my original or get an 5.0 as anything bigger is hard to get in here...
Engines running upwards of 11K RPM should be running 20-30:1 oil ratio (20 is better than 30 ALWAYS--> zero downside) and you need to run an oil that offers good protection at these higher RPM. This is critical!!
If you are searching for more power , cooler running engines, and longer bearing and piston life.... OIL will get you there.. Less oil= LESS life and less power.. and vice versa.
As you lower RPM (usually increase bore and stroke engines) you can lower the oil ratio (if you want) .I would never suggest EVER running less than 50:1 in ANY engine..
The idea that more oil , significantly, effects jetting is simply not accurate.. Switching from 50:1 to 32:1, for example, will not have any significant (read need to adjust jets) effect on jetting calibration.. I know.. Blasphemy... right?? but, true none the less..
currently I ride on a 125 TC 2017 with original settings
Main jet 480
Jet slows down 45
needles 43-74
s1
bushel 4.0
I only ride on ground temperature 5 degrees to 15 degrees at 100m elevation and the bike gouges at low speeds when the grip is fully open.
Do you have any recommended settings?
Post a reply to: 125/150/250/300 KTM/HUS/GG jetting thread