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Whats up guys. Needing a little help here with my 2022 KTM 250sx. In 2nd and into 3rd gear only, my bike has a weird bog and seems to only happen right after the mid-range when the powerband starts to kick in. I am running the setup below. I have the stock expansion chamber with the r304 shorty. I run straight AVGAS 100LL with Amsoil Dominator at 50:1 with PV about 1.5 in from all the way out with the standard PV spring. When I'm in neutral and warming up the bike it sounds so crisp and doesn't miss a beat, only occurs when I'm twisting the throttle wide riding on the track. Thank you! *stock reeds as well*
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #2
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 50:1
My bike is a 300 now, but when it was a 250 I had almost exact same specs as you also using straight 100LL. Except I was running a 37.5 pilot and the bike ran excellent. (40-60 degrees. Summer I ran a 35). I was also on 38:1 with Motul 800. Try the 42-75 needle on clip-2 at some point also. I went back and forth.
Would I need to mix it richer then with the 100LL? I will try the 35 pilot, I am here in FL so temps are around 70-80 at current. Riding Redbull day in the dirt this weekend so I will test it then! Appreciate it man!
I run the same, straight 100LL. I think with us running that fuel we need a little richer jetting than the specs on page 1.
With your temps I think 35 pilot will get you better. Then try that 42-75 on C2 when you have a chance just to know how it runs. Might be a bit better.
The Shop
Okay I will give it a try. Why did you run motul 800 at 38:1? Out of curiosity, what pipe setup are you using and which color PV spring did you use?
I run the 800 because it's very good oil and runs excellent. I have no experience with Amsoil but I hear it's very good. I believe that's what AJ did all the original settings with. I run 38:1 because Motul is a European oil and comes in liter bottles instead of quart bottles! It's just easier to do 500ml per 5 gal of fuel instead of 16 oz. That makes it a little more oil than 40:1 and takes it to 38:1. No other real reason for that than I also like more oil than 60:1 or 50:1. I also have a 125 that I run at 38:1 so it makes it easier to have 1 jug.
I am running an FMF Factory Fatty with Powercore-2 silencer (normal length, not shorty) and the stock PV spring at 1.25 - 1.5 turns in from all the way out.
Okay good deal man. is it a myth that more oil will create less power? I will try your ratio and oil for my next jug and see how she likes it. I definitely want the FMF system, will be getting soon. Would it be a possibility i was getting a lean bog with that 32.5 pilot? I never got the bog until I tried sunoco 110.
Basic old school 2-stroke wisdom is that more oil always creates more power. This is due to better ring seal and better lube on the bottom end. This assumes you are jetted for that ratio, of course.
Yes, totally possible you were getting a lean bog with too small of a pilot. When my bike was a 250 it ran very well on the 37.5.. even at slightly higher elevations like 1500ft.
Dang alright I will definitely give it a go then! So, the specs I am currently running, with a 35 pilot, should be sufficient for the Motul 800 @ 38:1 correct? Was there anything else you did to the 250?
Just to throw some info out there, the PC pipe and silencer made more power than the FMF did. In either case you want the long silencer.
currently 141 hours on the stock bottom and running 55:1 with 51 on this current top end.
Hey alright, are you running the standard 304 then? And what is your thought on the slight bog i am experiencing? Switched to a 35 pilot and im testing this weekend. running the 100LL @ 50:1 amsoil dominator.
I had a long reply typed out and the server had an error when I hit submit.
yes, the 304.
yes it could be a lean bog. Could also be a bog that the 1/2 clip position of the other needle FGR mentioned would fix. Thats what I had happen with me. I had the bog with straight race fuel which the 100LL runs similar. I also had a rich bog in between jumps that I had to drop the pilot one size to fix. I think I have the 35 in there now and the 37.5 caused the bog. I run the 37.5 when it’s below 40, anything over that I get the bog. And this is how my bike it, not saying that’s how yours would be as each runs a bit different and weather/location plays into it.
I switched out the mikuni for Keihin 38mm on all of my ktm 250/300s. Running 40:1 maxima K2. They run absolutely amazing. Smoother and more power everywhere plus much needed over-rev.
Have you have it on a dyno ? i would think that you are right that is maby smoother and more power down low but i think that the mikuni will have it coverd when its comes to overrev.
Did both the Keihin and the Mikuni on my 250/300 (and a few 125's). Keihin has a wider window of "acceptable" performance, i.e. is easier to nail a workable setting. Mikuni has better performance once dialed correctly with the jetting from this thread, especially overrev. With the Mikuni you may only be 1-2 steps off on jetting and pull your hair out before you ever get there though. So the Keihin is maybe a better first option for guys that don't especially like tinkering with stuff or care to learn a whole lot about jetting.
What’s your elevation and jetting on the 250sx?
always curious on keihin jetting
im at 42/Necj /175
thx
From memory, I think I was 48/175/N3EJ-2 with a 6.5 slide running 40:1 with avgas.
What jetting setup are you running on the mikunis, I tried almost everything. I tried a JD kit and it was an improvement but the Keihin worked better everywhere for me. On my 250xc I’m running the sx ignition, fmf fatty and 2.1 shorty, rk tech head, V-force V4R reeds and the red power valve spring. On my 300xc I’m running the same setup except a PC exhaust system. It’s not a lot of mods but it helps tremendously with overall power and over-rev.
Pit Row
Start on page-1 of this thread and go from there, lol. Here is where I ultimately ended up, all with straight avgas at 38:1 with Motul 800:
250:
PJ 37.5
Main 500
Needle 42-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5-1.75
300:
PJ 35
Main 500
Needle 43-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5-1.75
This is my bike with PC pipe and 304 silencer at the time running u4.4 at 60:1 with just the jetting from page 1. 2018 250sx
Im running the same set up as you from page 1. just move the needle up to #3 worked on mine for both my 250 and 125 they both responded well too the change on the AVgas, and is also working well with 2:1 91 Pump/ U4.4 36:1 Motorex
Good deal, I just moved mine to position 3 and i am testing tomorrow! Will also try to mix more oil and see how she likes it.
I’m still having the bog, it’s in the top end, PV at 1.75 in from all the way out, Air screw about 1.5. Is it possible I have a cracked reed? That’s all I can think as of now.
Ran c12 through it and the thing ran like a raped ape hahahaa. Avgas was the culprit for me. RIP my wallet now
Hi, do you have new jetting information for 300sx. I also have a 300 but I have difficulty adjusting it correctly, I drive it like a 125, in deep sand.
450
32,5
44-75 2nd position
A/S:2
Just what’s on the first page. You need the slide to make the jetting work, the stock one is too rich and there is no getting around that.
You can cut it 50/50 with pump gas to help cut the cost.
Yup, you need the slide like AJ said. Look a few posts above for what I am running in my 300. I am not riding deep sand but I feel like this jetting is on the "safe" side and would at least be a very close starting point to get you going. I'd be afraid to run a 450 main in sand !
300:
PJ 35
Main 500
Needle 43-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5 - 1.75
Motul 800 at 38:1 with 100LL AvGas
Im going to test, I have all of them and I also ride motul 800 39:1 and avgas100ll.
i test this in few days and go back to you.
thanks guys.
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