03 RM250- Need some help.

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.


35 pilot jet is too small.thats why it runs better with the air screw further closed.

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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