KDX250 Jetting

92_KDX250 · Feb 14, 2006

Had a look at my jets in my 92 250 and the pilot jet was a #55 (think the stock is #42 or something) which I thot to be too rich, i found a #48 pilot jet and installed it and now i cant get the bike to idle. The main jet is a #165 and the needle is the stock one with the clip 2nd from the top. Any ideas why i cant get it to idle? Ive tried playing about with the air screw but had no effect.

Cheers

TimberPig · Feb 14, 2006

Did you actually check to see if the pilot circuit was too rich, or did you just blindly change the pilot on a hunch? If it won't idle with the 48, and the air screw isn't doing anything, have you tried the idle adjustment (choke knob on some, slide stop screw on others)? Maybe you need to just put the 55 back in, and check to see if the jetting is actually too rich?

Try reading this to ensure you are doing it right. Jetting has to be done systematically by observation, not by making guesses on what you think should be in there without checking to see if it is correct or not.

Jetting Link

92_KDX250 · Feb 14, 2006

I'm trying to lean the mixture because its too smokey and it tends to feel as though its going to foul a plug when riding slowly, you need to rev the nuts out it to clear it out and it smokes like hell, the plug (b9es) is black and very wet and oily. I've read lots of reviews on the bike and i've heard the bike is too rich as stock, it also runs quite "chuggy" when the throttle is held at steady revs. Ive tried the idle screw turned all the way in and still doesnt idle. Also the bike starts 1st kick w/o the choke and idles fine when cold which makes me think its too rich (or perhaps my choke isnt working properly)

43Duc748 · Feb 15, 2006

This is what I run in my KDX250:

1367 needle, and 38/155-158 jetting
BR7es plug
I run my pre-mix at 40:1 (Yamalub 2r)

My bike smokes a little but runs like a bat out of hell.

I have more KDX 250 info on my webpage:

http://www.garage.whatburns.com/KDX2.htm

trevor morgan · Feb 16, 2006

I run a 160 main which is the smallest I could get from Kawasaki and a 38 pilot with a BR8EV plug. The bike runs well and is really quick when your racing around a practice track. If I try and ride at a steady speed then it does get chuggy, i think you will find this with most tuned 2 stroke off roaders, I've had a couple of road legal MX bikes and they were both like that. The 48 pilot jet you have installed still sounds massive to me, I'm sure mine had a 42 standard, I'm wondering if someone has maybe changed the carb?

92_KDX250 · Feb 16, 2006

Gony try the bike shop tomorrow and see if i can get a 38 pilot and a 160 main, im running a b9es plug so mite try the br8ev, what needle and what clip is yours on trevor?

trevor morgan · Feb 16, 2006

I run a standard needle 2nd clip from the top. If your going to buy some jets then you may as well get the 1367 needle like 43DUC748 suggested as this seems to be what most people who know anything about these bikes and the way they are jetted advise, I ought to change mine but haven't got round to going to dealer. I run 40:1 with Motul oil, Kawasaki reccomend 32:1 but my bike smoked like a chimney. If you run on Silkolene then change to Motul, Its more expensive but greatly reduces the white smoke. I changed the plug to a BR8EV simply because it was fouling the standard when pottering around, I know people will say that points to jetting being rich but the new plug makes it a crisper throttle responce, the colour is good and reduced plug fouling.

92_KDX250 · Feb 16, 2006

Ok, i'l try and get a 1367 needle and 38/158 jets.
Also i just noticed that the stock needle should be R1368H, and mine had R1368J, does this mean my needle has been changed b4? (I'l be getting a new R1367H anyway)

trevor morgan · Feb 17, 2006

Before you go spending any money at Kawasaki check this out. Just been on to the Buy Kawasaki web site to check where the R1368J needle you have comes from. The needle and the jets you have come from an 89 KX250 !! Now this means that someone has either put this carb on your KDX engine or you have in fact got a complete KX250 engine set up in your KDX frame. I suggest you check out some part numbers and engine numbers and see what engine you have.

Matt90GT · Feb 17, 2006

The jetting is way off on that bike.

I would first get the KX head gasket that is thinner for more compression and that will give you a bit more power. Only take about 20 minutes to install.

For the jetting, this is what I ran on my bike:

Jetting: 38/158 , R1367H needle 3rd clip from top, #6 slide

No smoke, no issues. I was also running the amsoil premix @ 50:1 with that jetting. It ran really strong, especially with a 50/50 racegas mix.

dirt bike dave · Feb 17, 2006

trevor morgan said:
Before you go spending any money at Kawasaki check this out. Just been on to the Buy Kawasaki web site to check where the R1368J needle you have comes from. The needle and the jets you have come from an 89 KX250 !! Now this means that someone has either put this carb on your KDX engine or you have in fact got a complete KX250 engine set up in your KDX frame. I suggest you check out some part numbers and engine numbers and see what engine you have.

Good research, Trevor. The '91-94 KDX 250 is based on the '88 and '89 KX250. Someone could easily drop a KX motor of that vintage into the KDX250. I think the KX carb slide also has 1mm more cutaway than the KDX slide. The extra cut-away is an improvement over the stock KDX slide.

If the bike still has a lighting coil, my guess it is a KDX motor with a KX carb.

pete fry · Feb 18, 2006

If you phone Corby Kawasaki with your engine and frame numbers they will tell you what you have got.Their number is in T&MX news.I order all my parts from them and would recomend them,they always seem to have what you want in stock.Allens Performance are the people for carb parts.Hope this helps.

92_KDX250 · Feb 18, 2006

Its a defintly the original kdx engine, not so sure about the carb but the engine number starts off with dx250....... and it has a lighting coil with a big heavy flywheel. Got some new jets yesterday, could only get 40 pilot, 160 main, they didnt have the needle in stock so i just installed the new jets and my stock needle and its made a big difference! Will idle now with the air screw at 2.5 turns out (so still a bit rich) ridden it all day today going slow, flat out and its alot better, very little smoke and it didnt eat the spark plug.

oh my head gasket if from a kx250, not sure what year tho.

dirt bike dave · Feb 18, 2006

The '88 KX250 head gasket is the thin one that you want to use. '89 and I think '90 KX250 fit, too. One of those years has optional thick and thin gaskets. For '88 there is only 1 part # available and it's thinner than the KDX gasket.

Kawasaki did a horrible job jetting the KDX250. The bike is so much better with good jetting. Since you are fiddling with the carb, you should check and see how much cutaway the slide has. There will be a # and a star stamped on it. Stock is either a 5 or a 6mm cutaway, can't remember for sure but I think it is a #5. You want the slide that has 1mm more cutaway than stock. If you have a KX carb, you may already have the right slide.

92_KDX250 · Feb 18, 2006

my slide has a 5 stamped on the top of it

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