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03 RM250- Need some help.

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My 03 rm250 has a sputter off idle until about 1/4 throttle. The rest of the throttle range is fine.

Current Jetting:

150 main

35 pilot

No. 7 slide

Stock N8RH needle at top clip position

With the air screw at 1/2 to 3/4 turns out it seems to run better than 1-1/2 turns but the idle is highest at the full 2 turns out.

Castor 927 at 40:1 with 100 octane

I've tried the n3ej and n3ew needles but they don't seem to do the trick. The elevation is about 2300' and 100 degrees. There is a smalll amount of spooge out of the silencer but I can live with that. The sputter I can't. The plug is not overly saturated but is black. I've been through all the posts on TT and my situation seems to be unique as I have not seen anyone with a pilot and main this small. I was thinking that I need a needle with a leaner diameter at 1/4 throttle but I dont want to keep spending money on stuff that is not working. Should I go down on the pilot again? Is there another needle that I need to try other than the ones I already mentioned? I would like to have the needle at the 2nd or 3rd clip so that I can go leaner when I take trips to higher elevations. My buddies jd red needle for his 98 ktm 300mxc works the best out of the needles that I have tried so far but it was still not right.

Maybe I am just not understanding the proper way to jet my bike. I've read Spanky's jetting guide and have read all the advice given in the jetting forum and I am still stumped.

Any suggestions or advice is appreciated.


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The stock jetting that your bike came with (175 main, 48 pilot, N8RH needle 3rd clip from the top, 6.5 slide, and #50 power jet) ran rich at 70 degrees and 0’ elevation and will only get worse as temperatures or elevations climb above 70 degrees and 0’ elevations. For your current conditions I would recommend that you purchase a 42 pilot, a 155 main, and a #48 power jet. Set the clip on the stock N8RH needle to the #1 position. You have already purchased the most expensive component, the 7.0 slide. Start with the airscrew at 1-1/2 turns out and you should be within a 3/8 of a turn + or – of the correct setting.

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