2003 KX 125 Jetting Advice

BobPA
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BobPA
So I have usually been pretty descent at dialing all of my bikes, jet skis, and snowmobile in. But this little Kawi is beating me up. Quick run down

Eric Gorr 144 with 1.5 hours of mostly break in
Top end porting with race gas compression
New crank seals
All new gaskets
New Boyesen reeds
Stock pipe with pro circuit shorty
VP U4.4 oxygenated fuel
700-1500 feet elevation

Stock
Main 420
Pilot 40
Clip 2nd stock needle

For the fuel/compression/porting I am running I figured I'd start it way rich just to be safe so I went

Main 450
Pilot 40
Clip 4th stock needle
Air screw is currently irrelevant

After break in I started getting on it and it was feeling pretty rich down low transitioning to a flat midrange and flat top end. I bumped the pilot down and it helped a bit. Dropped the needle and it helped the midrange a touch. But doing a plug check reveals what appears to be a fairly lean condition up top, which is confirmed by the flat feeling on top by my butt dyno. I do not have a 460 main to try as my kit only goes to 450, but I will get one tomorrow.....along with a 470

My issue is the rather blubbery bottom end was not really cleaned up by the smaller pilot, currently 37.5. I am going to grab a 35 and 32 tomorrow...so would you guys go 460 main with a 35 pilot? Never do I remember running such a large main in any of my old 125's....then again I never ran U4.4.

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ricko
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ricko 4/17/2017 12:15pm
4/17/2017 12:15pm
I don't have a 144 kit but mine is ported, lots case work, boysen reed cage, pc pipe and shorty silencer, running renegade sx2, I am also in PA, I am running 37.5 pilot, 410 main, and stock setting on the needle and mine is absolutely crisp. Doing some reading some people switch out the carb for a Keihn since what we get stuck with stock is hard to tune.
BobPA
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BobPA 4/18/2017 9:12am
4/18/2017 9:12am
ricko wrote:
I don't have a 144 kit but mine is ported, lots case work, boysen reed cage, pc pipe and shorty silencer, running renegade sx2, I am...
I don't have a 144 kit but mine is ported, lots case work, boysen reed cage, pc pipe and shorty silencer, running renegade sx2, I am also in PA, I am running 37.5 pilot, 410 main, and stock setting on the needle and mine is absolutely crisp. Doing some reading some people switch out the carb for a Keihn since what we get stuck with stock is hard to tune.
I am going to play around with it this week. It is really kicking my ass haha
Rocket164
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Rocket164 4/18/2017 5:20pm
4/18/2017 5:20pm
Try running the needle in the 2nd or 3rd clip position. If it gets better put the 40 pilot back in. I think your needle is too rich and your trying to compensate with a leaner pilot. I just went through this on my YZ125 and I wanted to pull my hair out thinking the pilot was too rich. Ended up being my needle was 1 clip position too rich and tricking me into thinking it was the pilot.

I would try running this jetting with the oxygenated fuel......450 or 460 main, 42 pilot, stock needle in 2nd or 3rd clip. this is what's recommended in my mod YZ125 with oxy fuels. I know I know, you have a KX but I think it will be similar.
BobPA
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BobPA 4/18/2017 9:26pm
4/18/2017 9:26pm
Rocket164 wrote:
Try running the needle in the 2nd or 3rd clip position. If it gets better put the 40 pilot back in. I think your needle is...
Try running the needle in the 2nd or 3rd clip position. If it gets better put the 40 pilot back in. I think your needle is too rich and your trying to compensate with a leaner pilot. I just went through this on my YZ125 and I wanted to pull my hair out thinking the pilot was too rich. Ended up being my needle was 1 clip position too rich and tricking me into thinking it was the pilot.

I would try running this jetting with the oxygenated fuel......450 or 460 main, 42 pilot, stock needle in 2nd or 3rd clip. this is what's recommended in my mod YZ125 with oxy fuels. I know I know, you have a KX but I think it will be similar.
Thanks, I was thinking the same thing today at work. The bikes are different, but my friend has an 04 RM 125 with incredibly similar jetting setups to ours. I am going to do a test session tomorrow after work, Ill throw up some plug pics.

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HenryA
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HenryA 4/19/2017 4:17am
4/19/2017 4:17am
Never went pass 420 in my KX and she had a full race spec engine. 125 though....
What plug are you running? Any work done to the head?

Idk, 470 sounds very rich. I was under the impression that you would want to go a size down on the main jet when you went big bore? But on the other hand, never jetted a KX144 myself.
BobPA
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BobPA 4/19/2017 7:00am
4/19/2017 7:00am
HenryA wrote:
Never went pass 420 in my KX and she had a full race spec engine. 125 though.... What plug are you running? Any work done to...
Never went pass 420 in my KX and she had a full race spec engine. 125 though....
What plug are you running? Any work done to the head?

Idk, 470 sounds very rich. I was under the impression that you would want to go a size down on the main jet when you went big bore? But on the other hand, never jetted a KX144 myself.
Head is spec'd for 105+ octane. Eric gives no literature when he send back your completed engine. Going to check squish tonight and play around a bit more. The U4.4 is oxygenated...that is why I started with such a large main, safety because I have zero experience using it.

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