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2004 kx250f Jetting issue-seperated shoulder

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Fmf power up jet kit has me stumped and my shoulder seperated lol My bike like every other kx250f popped on decel, so I fig I'd start with a jet kit and put a 42 pilot in (stock 40), ordered an fmf kit and to my demise it did not include pilot jets, not frazzled I fig why not put it in and see what happens. Put in the new needle, clip on 4 and rec 155 main for my altitude which seems weird as stock is 178 but maybe the needle is a smaller diameter shaft to make that ok?? also put in mixture screw I've been meanin to put in while I had the carb out. Excited woo test drive, major increase in power bottom to top, not a single pop!!! Holy shit somehow maybe this worked!! Elevation 952 ft temp 85 or so. I'm stoked, load up the next morning head to the track elevation 954 temp 82 degrees. Gear up hit the track, track is wet muddy and rutted... First lap start noticing a sputter on wot accel through the mud and sputtering on jump faces. Also off idle bog if snapping the throttle.. Back to the pits on the stand readjust mixture screw a little richer hoping to help the off idle bog, confused, now the fun part....... Hit the track seems good, first two corners powered through, hit the first big table wide open! 3/4 up the face sputters and cuts out! Immediate nose dive grade 3 ac seperation in my left shoulder lol So! What happened? Bike ran great other than popping on decel. Maybe the increased load from the mud? Should I try needle clip on pos 3? Any advice would be appreciated lol I do have 6 weeks of physical therapy to look forward to so time is not an issue lol thanks! First post!

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Little more info, switched back to stock jetting and needle today and problem is resolved however popping on decel has returned lol maybe a 42 pilot is the direction I need to head down

Edited by pquack86

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I have and at 3 turns out it still pops a little that's why I originally wanted to try a 42 pilot, the fmf kit unfortunately did not come with one

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I have and at 3 turns out it still pops a little that's why I originally wanted to try a 42 pilot, the fmf kit unfortunately did not come with one

Have you inspected it to make sure the o-ring is perfect?

If you are at 3 turns out, you have an air leak somewhere, like the oring, carb boots, header, pipe junction, bad muffler packing, etc.

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I put a new extended adjuster in, still same result so that rules out the oring, I'm with William I think my pilot circuit is running lean and a 42 should do the trick, I repacked the muffler on Sunday after straightening it back out from my failed front flip attempt lol I also found a link that compared the fmf jet numbers to the stock numbers https://thumpertalk.com/topic/638069-fmf-vs-jd-jet-kit/

If those are correct then the fmf 155 is similar to a stock 171 jet considerably leaner so that was prob why it was sputtering on wot on jump faces... I'm going to try a 42 pilot and then ill get a new plug and see how my main jet looks

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If you have some popping on deceleration that is normal.

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Update!! So been meaning to order a 42 pilot and hadnt gotten to it, cleaning out the garage tonight found a package that came with my wife's yz85, low and behold! Jets!! 42 pilot!! Swapped in the 42 pilot, played with the air/fuel screw, settled on 2.5 turns and test ride! Fixed!! Thanks guys!!! Shoulder is feeling better too!

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