18' 250sx, jetting, spark plug colors, NO TOP END power

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1/3/2019 2:27 PM
Edited Date/Time: 1/3/2019 6:22 PM

Did the platinum pipe and longer of the two 304 silencers hoping to get some top end all it feels like is very slightly less bottom end. Same tank of gas same place same conditions and 38*F temperature.

pulls like a wild animal on meth thru the midrange then falls off a cliff for last 20% of rev range...

please help

bike has 2 hrs,
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1/3/2019 2:41 PM

I have fmf factory fatty & powercore silencer, 1-2 step richer main jet, 1 less tooth on rear, top end pull is pretty good. Was the PC pipe supposed to allow more overev?

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1/3/2019 3:01 PM

What jetting are you running?

And what power valve spring and turns in?

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1/3/2019 3:19 PM

sandman, yes gents on here said just the silencer even made a quite surprising difference if you didn't have the $ for the pipe at same time, also there was a mag test with it saying it added 4+hp on top end.

erik,
stock jetting, bike has 2hrs on it, checked it all 4 times I rode it plug looks pretty good. all been in 32-40* F temps so not as rich as it will be during the spring. also to my understanding and the manual/videos the PV adjustments do not make any changes at all to anything above the midrange into the top end/over rev. the PV positioning is untouched from factory

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1/3/2019 3:21 PM

I think it's most likely lean on top and you could feed it more fuel with a richer main jet!

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1/3/2019 4:34 PM

seth505 wrote:

I think it's most likely lean on top and you could feed it more fuel with a richer main jet!

Agree, try the next few steps richer main jet, it helps the top end pull, it's lean from the factory, it will be more lean in cold temps, the colder temps will help the rich pilot...I feel my 18 had a rich pilot jet and lean main ...I am 2 steps leaner pilot & 1-2 steps richer main changing the needle clip position did not help me.

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1/3/2019 5:04 PM

GCBC wrote:

sandman, yes gents on here said just the silencer even made a quite surprising difference if you didn't have the $ for the ...more

PV positioning will make a difference in the top end id it stays closed. Make sure it is functioning properly.

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1/3/2019 5:06 PM
Edited Date/Time: 1/3/2019 5:09 PM

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1/3/2019 5:31 PM

Definitely start by adding a bigger main jet and idk about the newer motors but my 14 had terrible squish that needed fixing as well as being lean

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1/4/2019 12:32 AM

Also looking at your plug pics I usually preferred a little more brown to the plug. I think yours are a tad lean. If u can run a wide open run for a few seconds then hit the kill switch, pull in clutch and use brakes but keep the throttle held wide open until you stop then check plug. I would go up probably at least 2 sizes first though, I usually go 4 up and work down.This will tell you what the main jet looks like and then do the same for half throttle.

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1/4/2019 5:54 AM
Edited Date/Time: 1/4/2019 5:55 AM

This is the jetting I had with C12 in the mid 60*'s
MJ 470
PJ 32.5
Slide 5.75 (stock is 4.0)
Needle 42-75
Clip 4th position
Needle jet s-4 (stock is a s-1)
AS 2.0
C12 mixed 60:1 with amsoil donionator
Elevation 560'

The Jetting thread

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2018 KTM 250sx
Instagram CamaroAJ

1/4/2019 6:13 PM
Edited Date/Time: 1/4/2019 6:41 PM

Thanks for your assistance so far guys, I went from a 440 to a 450 and don’t change anything else. It was same temps fuel and conditions today’s test and I am pleased to report it feels like it has a little more top end as it’s not falling quite as hard on its face. Perhaps I need to step up one more to the 460?
Unfortunately I ran the bike out of gas so looking at the plug after multiple 4rth gear pulls in the front yard was botched by it bogging and trying to get it to get it halfway up my 1000ft super steep driveway.
That said plug was darker and blacker around the ceramic

Will not be able to test Saturday due to rain. I believe I am going to twist the PV adjuster all the way out as a test

*edit, I suppose I should try the jetting first before making the mech SoCal change of PV adjustment to keep it one thing st a time

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1/4/2019 6:21 PM

go to a 460

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1/4/2019 6:26 PM

sandman768 wrote:

I have fmf factory fatty & powercore silencer, 1-2 step richer main jet, 1 less tooth on rear, top end pull is pretty ...more

exactly what i did.. especially with the cold. you need a richer main jet

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1/4/2019 6:26 PM

AJ565 wrote:

This is the jetting I had with C12 in the mid 60*'s
MJ 470
PJ 32.5
Slide 5.75 (stock is 4.0)
Needle 42-75
Clip 4th position
...more

Straight c-12? Have you had any work done to your head?

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1/5/2019 3:06 AM

Might sound dumb but are you running the platinum or platinum 2 pipe?

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1/5/2019 4:36 AM

chump6784 wrote:

Might sound dumb but are you running the platinum or platinum 2 pipe?

Not dumb at all.....if he is running the woods pipe he will never get top end!

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1/5/2019 6:43 AM

AJ565 wrote:

This is the jetting I had with C12 in the mid 60*'s
MJ 470
PJ 32.5
Slide 5.75 (stock is 4.0)
Needle 42-75
Clip 4th position
...more

sandman768 wrote:

Straight c-12? Have you had any work done to your head?

No engine work at all. That was my C12 jetting, I now run straight u4.4 and have different jetting for that.

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2018 KTM 250sx
Instagram CamaroAJ

1/5/2019 9:54 PM

chump6784 wrote:

Might sound dumb but are you running the platinum or platinum 2 pipe?

platinum regular. I was told its same as the works pipe but didn't like the finish on the works pipe. switching to a 460main tonight going to retest tomorrow and report back!

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