2017/2020 ktm 250sx carb swap to Keihn 38 air Stryker

whiteman60
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whiteman60
So how many of you have switched from the factory carb to the Keihn with great results. My Mikuni is jetted well but feel I could benefit from the Keihn. Is there much to gain or is it just a waist of money. I had suck good luck with the old carb on my 300sx I built a few years ago. I set it and never had to touch it. I just want to know what others have done and what jetting this new bike likes with the Keihn carb. Already know if prob use the old necj needle from the past.
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mwmx54
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mwmx54 5/5/2020 9:01pm
5/5/2020 9:01pm
I put a 36 keihin from a 2016 250sx in my 17 300, I’m no pro carb guru by any means, I just got sick of dicking with my carb every time I went riding, and as the day went from hot to cold, or dry to wet. I really just missed not having to touch it ever, like on my old 2014 300. I now have that reliable no need to mess with the air screw and it always fires right up hot or cold. The best part though, is that I got a domino throttle assembly, it’s buttery smooth compared to the new crap they come with. This isn’t to say the mikuni doesn’t work, it worked great once I got it dialed in, I just always had to atleast adjust the air screw, and often times had to move the needle clip or main jet a size or two, but I didn’t notice much in power gains between the keihin, and the mikuni (once it was set up). I’ve heard the 38 does add some more power though, and I run the necj Suzuki needle, it works great.
brooklynevans 5/6/2020 12:35am
5/6/2020 12:35am
I’ve made the swap to Keihin on a 19 250sx. NECJ needle, 42 pilot - runs really clean.
seth505
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seth505 5/6/2020 7:16am
5/6/2020 7:16am
I did a lot of tinkering with the Mikuni but once I got it good I hardly have to touch it other than the air screw.
whiteman60
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whiteman60 5/6/2020 7:31am
5/6/2020 7:31am Edited Date/Time 5/6/2020 7:32am
I do have mine dialed pretty good. Did the
5.5 slide
42/75 needle
s4 needle jet
32.5 pilots
490 main
AS 1.5
60:1 ratio
Also did the float bowl mods and straighten the overflow tube a bit and put a loop in overflow tub.
Bike runs really good no exhaust drilling
Runs clean good power.
I feel like my older 250 had way more pick up down low with the 36 keihin.
I contacted Dicks racing who did up all my carb and head mods on my 300 sx. Having him get me a 36 air Stryker carb and going to have him do same mods as last time 36/39 taper bore and the torque wing. My old bike just had that instant power where I notice there is just not much response at initial throttle opening with the 38 carb I think when they went to the 38 they lost the instant response the 36 had at 0 to 1/4 throttle. My Mikuni is working great but just feel there is something missing at that low rpm. I like really quick response off bottom.

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AJ565
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AJ565 5/6/2020 8:59am
5/6/2020 8:59am
whiteman60 wrote:
I do have mine dialed pretty good. Did the 5.5 slide 42/75 needle s4 needle jet 32.5 pilots 490 main AS 1.5 60:1 ratio Also did...
I do have mine dialed pretty good. Did the
5.5 slide
42/75 needle
s4 needle jet
32.5 pilots
490 main
AS 1.5
60:1 ratio
Also did the float bowl mods and straighten the overflow tube a bit and put a loop in overflow tub.
Bike runs really good no exhaust drilling
Runs clean good power.
I feel like my older 250 had way more pick up down low with the 36 keihin.
I contacted Dicks racing who did up all my carb and head mods on my 300 sx. Having him get me a 36 air Stryker carb and going to have him do same mods as last time 36/39 taper bore and the torque wing. My old bike just had that instant power where I notice there is just not much response at initial throttle opening with the 38 carb I think when they went to the 38 they lost the instant response the 36 had at 0 to 1/4 throttle. My Mikuni is working great but just feel there is something missing at that low rpm. I like really quick response off bottom.
Whats your power valve set to? If you haven't messed with it yet run the stock spring at 1 3/4 turns in from all the way out and see if that takes care of your low end pull.
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whiteman60
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whiteman60 5/6/2020 9:15am
5/6/2020 9:15am Edited Date/Time 5/6/2020 9:16am
whiteman60 wrote:
I do have mine dialed pretty good. Did the 5.5 slide 42/75 needle s4 needle jet 32.5 pilots 490 main AS 1.5 60:1 ratio Also did...
I do have mine dialed pretty good. Did the
5.5 slide
42/75 needle
s4 needle jet
32.5 pilots
490 main
AS 1.5
60:1 ratio
Also did the float bowl mods and straighten the overflow tube a bit and put a loop in overflow tub.
Bike runs really good no exhaust drilling
Runs clean good power.
I feel like my older 250 had way more pick up down low with the 36 keihin.
I contacted Dicks racing who did up all my carb and head mods on my 300 sx. Having him get me a 36 air Stryker carb and going to have him do same mods as last time 36/39 taper bore and the torque wing. My old bike just had that instant power where I notice there is just not much response at initial throttle opening with the 38 carb I think when they went to the 38 they lost the instant response the 36 had at 0 to 1/4 throttle. My Mikuni is working great but just feel there is something missing at that low rpm. I like really quick response off bottom.
AJ565 wrote:
Whats your power valve set to? If you haven't messed with it yet run the stock spring at 1 3/4 turns in from all the way...
Whats your power valve set to? If you haven't messed with it yet run the stock spring at 1 3/4 turns in from all the way out and see if that takes care of your low end pull.
Yes I have copied all your specs. I feel that it’s got good power and it crisp but just might have gotten spoiled with my old bike and then when I did that 300 sx its was the best power I’ve ever felt from a 2 stroke. FYI I raised port timming on that 300 and had dick wilks cut head back down to bring compression back up and had him do the Chanel’s in the head his torque mod and That engine still reved good on top too. Back to my 250 I believe my old 250 just had more of that initial roll on power. This bike may just have a different power band to rev more on top.
I don’t believe it’s a carb running issue it’s just the way it is with a bigger carb have to give up something to gain something.

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