hanging idle with 5.75 slide

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5/4/2018 6:50 AM

Installed 5.75 mikuni slide on bike (17 250sx). Bike runs fantastic on MX track for 4-5 minutes then develops a nasty hanging idle. Track is similar to southwick (sandy), just curious where to start?
current specs are:
37.5 pilot (42.5 stock)
43-73 needle clip 3
450 main
a/s 1 turn out

Needle issue or PJ?
Should I try 1 clip richer on needle or go to next richer needle?
Seems like anytime I get it to run perfect (Crisp?) I get a hanging idle after 4-7 minutes...thanks for the input

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5/4/2018 6:59 AM

Hanging idle is a lean condition. Right off the bat your pilot is small. Increase the size & Check for air leaks. Then once thats dialed (youll know when your air screw is 1.5 turns out at the highest idle) go to the needle. Then main jet.

Also you need to let the bike warm up before jetting. That 5 mins on the track is about the time it takes to warm up fully.

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5/4/2018 1:01 PM

What Needle Jet are you running?

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5/4/2018 3:28 PM

What jet needle are you using,s-1 or s-4, and at what temp were you riding when the hanging idle happens?
,

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5/4/2018 4:55 PM

S1 (stock)
65 degrees

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5/4/2018 7:17 PM

With that slide and jetting you need the s4 needed jet. I’m running the same jetting except I have the s4 and a 490 main jet (460 with C12, but the 490 with T2 or u4.4) and no hanging idle.

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2018 KTM 250sx
Instagram CamaroAJ

5/4/2018 7:46 PM
Edited Date/Time: 5/5/2018 2:37 AM

Like AJ said, you need an s-4 needle jet, especially when using the stock needles with the leaner slide. With the s-4 you are going to more than likely need to use a leaner pilot jet as well. I also notch the front of the slide, which makes the pilot circuit a little more efficient, and most times requires the use of an even smaller pilot jet.

s4 needle jet--,KTM part#---- 55431021400

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5/4/2018 9:45 PM

Here are my jetting notes for Nonoxyganated race gas for reference. Listen to digger, he’s who helped get my bike to where it is and it’s amazing.

MJ 470
PJ 32.5
Needle 42-75
Clip 4th position
Needle jet s-4
AS 2.0
C12 mixed 60:1 with amsoil donionator

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2018 KTM 250sx
Instagram CamaroAJ