2000 KX250 Jetting help

Hey Guys

I was doing some very tight, rocky downhill trails and never got to rev the bike up for about 2 miles. It eventually died and would not start again. I believe I fouled a plug and that it is jetting related.

If anybody can point me to a jetting chart or offer up some advice for my elevation (5250 ft) as well as sea level, it would be greatly appreciated.

Current setup (stock bike):

155 MJ

48 PJ

Needle N3YF clip 1

I want to get the correct jets and needles for my elevation and sea level and prefer not to have to buy a whole range because everything here is imported and VERY expensive so any help would be great!


I'm not sure about the elevation, but you could go slightly leaner on the pilot and move the needle. What sprockets are you using? I run stock jetting with a 12t front sprocket and stock pipe, seems to work fine on tight stuff. I do clean it out every once in a while if I hear it bogging a bit.

I don't normally do the very tight stuff and thus run 15-49 for a more enduro style setup. I will go back to 13-49 when my sprockets are toast (soon).

Moving the needle up will make it richer if I am not mistaken?

I found a parts diagram on the Kawasaki website and it indicates the following stock parts and alternative options:

MJ: 160 - Options: 155, 158, 162, 165, 170

PJ: 52 - Options: 48, 50, 55, 58

Power Jet: 48 - Options: 42, 45, 48, 50, 52

According to this I have the leanest setup already? Part from the needle where I am not sure which code is leaner or richer.

Also I am not sure what Power Jet I have installed. Will have to check.

I run the 45 pilot and some times the 42 but I am a 5000' all the time. Check your reeds, if they have bad sealing it will cause it to run rich in the lowend and foul plugs too.


I don't normally do the very tight stuff and thus run 15-49 for a more enduro style setup.

:lol: I'd run those gears to commute to work! I'm using 12-48 on both my bikes to compensate for the :p up first gear. It actually works out pretty good for me both trails and MX. For the trails I can click 2nd and once in a while 3rd. With the stock 13-48 I was barely clicking 2nd. I think you may be lugging it waaay too much with that 15t sprocket, heck you probobly didn't even get off the pilot jet. lol I'd definately swap those sprockets and check the reeds like Ed said.

Can you even run a case-saver with that 15t sprocket?

I agree that I was lugging it quite a bit, lol, otherwise I would have ended on the rocks or those damn thorn bushes.

So you recommend 12-48 rather than 13-49? And yes, the case saver fits fine.

I will take out the reeds and give it a good cleaning and see if they need replacement.

Ed, I see from one of your other posts that you use a 152 MJ? Would you recomment the same for my model KX?

I need to add to this that I have for the first time used a new 2T oil for the premix. Same ratio though as always (32:1), maybe she wasn't happy with that brand oil :p

The 12 on the front will make a world of difference. Yes you will loose top speed, but who needs to go 65mph in the woods? I'm running the 48 because that's what I had at the time and I don't like to confuse myself more than I already am. Plus I can swap wheels between the bikes if I need to without issue.

The new oil may or may not be part of it. My buddies YZ fouls plugs like mad in colder weather using Maxima. We both run H1R now 365 without issues.

I dont claim to be an expert, but based on what I read in your description, I would not touch the jets for a idle or near idle plug fouling. I would turn the air screw out one turn.

Since you were going downhill in tight woods, I would guess that you were using either idle or very small throttle. In the 03 KX250 manual, it suggests that the air screw is mainly responsible mixture settings at that throttle range.


What is your air screw setting? My manual shows default setting is 2 turns out. The adjustment for 5250 feet would be somewhere between another 1/2 to full turn out depending on temperature.




cxcmoto, thanks for that!

According to those charts (with correction factor 0.92) I need a 152 mj, 48 pj, needle clip 1 and air screw at 3 turns. I am assuming the model KX those charts relate to is similarly setup to my 2000 model.

I also checked my reed valves and 3 of them seal properly and one has about 1mm gap. Is that significant enough to have to replace?

If you fouled your plug when riding in tight stuff dont change your main jet , your pilot and or needle should be changed, try a 45 pilot jet and you my have to get a leaner needle .

I also checked my reed valves and 3 of them seal properly and one has about 1mm gap. Is that significant enough to have to replace?


Replace the reeds and your gearing before you dig into the carb. If you still foul plugs then look into leaner jets. But right now both the reeds and gearing are problems that need to be fixed.

This is a very bad pic, sorry. But if you look closely you can see the small gap in the top right reed.


Any recommendations on aftermarket reeds or should I stick with OEM?

If you have only fouled 1 plug, at high elevation, while at idle or near idle for an extended period of time, I would not change a lot. If your air screw is currently at 2 turns out, I would only change the air screw to out 3 turns. Then do some testing. If you ride continuously at high elevations and still have issues, continue to make small changes. Keep a spare plug/wrench with you just in case. Just remember which setting controls which throttle position and make changes to the one that is causing issues.

Or, -- just pull in the clutch and rev it up for a 10-15 seconds every minute to keep it clear !!

This is a very bad pic, sorry. But if you look closely you can see the small gap in the top right reed.


Any recommendations on aftermarket reeds or should I stick with OEM?

Holy s.hit! A camera worse than Arts! :p

Holy s.hit! A camera worse than Arts! :lol:

HAahhahahaahaha :p

It's an X-Ray machine dammit !! :cry:

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