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09' Needle Jet advice- Am I still running lean?

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Hey everyone..two weeks ago I bought a used 2009 KX250f off craigslist and I am having some issues getting the jetting dialed in. The bike has Pro Circuit ti valve-train, cams, piston, exhaust and its been ported. I also using 50% cut VP C12 fuel. The bike came with completely stock jetting .. 182 main, 40 pilot,etc.

The first time I rode the KXF, it was clearly running really lean because it was popping, shooting flames at night and had trouble running at idle. I just replaced the exhaust gasket and the carb boots are secure so no leaks that I can see. After that I got online and order several pilot and main jets from Rockymountainmc.com.. which BTW are $3/piece...👍

So far I've tried a 42 & 45 pilot, every main from 175 to 182 and every position on the stock needle. But I still believe I am running lean. Currently I am using the stock 182 main, 45 pilot, and lowest clip on the stock needle. The 42 pilot, as suggested by most people here, runs dangerously lean even with the other rich settings. And If I back off the stock needle even one clip it will violently pop when I let off the throttle.

With my current settings (182, 45, lowest/richest needle position) It accelerates well without much hesitation, but when I let off the throttle after being HIGH in the RPM's, it pops in succession. The popping occurs after I release the throttle slightly or completely let go. Im going to say that the popping occurs when the slide is somewhere below 1/2 way of being fully open. Also When I go slow in 1st or 2nd, not going past 1/4 throttle, it runs great with no hesitation or popping. Additionally, the bike starts up first kick usually and idles flawlessly.

I am thinking that I need a richer needle to compensate for the motor mods.

I'm also going to order some even richer main & pilots just to mess with but I don't know which needle I should get? Or where to get it? Or is it possible I am overlooking something else? Perhaps the Leak Jet?

Thanks for everyones help!

pCp🤣

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Hm, well does someone know which needles are richer than stock?

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Its the needle specs.

I thought you were looking for a richer needle?

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Its the needle specs.

I thought you were looking for a richer needle?

I forget which one it is, but Pro Circuit and MXA recommend a different needle (as well as main and pilot) that is a honda part number. It is listed on PC's website. It is like $22. I haven't tried it myself though.

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Its the needle specs.

I thought you were looking for a richer needle?

Your right, I am looking for a richer needle. However, from that link I can't determine which needle would be richer than stock. I just don't have a basis for the spec. data. Currently I am at the richest setting on the stock needle and still experiencing decel popping and backfiring.

I have heard of people using the NCYS, NCYU, NCYR, etc. but I don't know which of these needles are richer or leaner.

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Decel popping happens in the PJ fuel screw area of the carb. If a 45 didn't work I'd go one above that.If you need simplicicty with a bicthen needle I'd get a JD kit. All so are you sure the fuel screw isn't missing a oring or washer? Where is that set at? All so check the pipe real good for a crack.

Good luck.

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Your right, I am looking for a richer needle. However, from that link I can't determine which needle would be richer than stock. I just don't have a basis for the spec. data. Currently I am at the richest setting on the stock needle and still experiencing decel popping and backfiring.

I have heard of people using the NCYS, NCYU, NCYR, etc. but I don't know which of these needles are richer or leaner.

Leaner to richer.

NCYU-NCYS-NCYR

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I believe my adjustable air screw only has an oring on the aftermarket piece itself and a spring. I was unaware of a washer and separate o-ring. Could this possibly be why its acting like it is running lean? If so, does anyone know the I.D. and O.D. to the washer and o-ring.

Thanks for your help stallion.

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