1991 KDX 250 Carb specs

Discussion specific to the 1991 - 1994 KDX250 sold in the USA
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Tinie
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1991 KDX 250 Carb specs

Post by Tinie »

Could anyone please provide me with the factory specs. for the Carburetor on my 1991 KDX 250.
Main jet size?
Needle nr.?
Slow jet size?

There is a lot about this topic on the forum, but somehow I can't seem to find the factory (standard) specs.

I already got the specs for the float level (height)
Asewell
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

This is from my Cyclepedia kdx 250 Service Manual Supplement,
Keihin PWK 38
Main Jet 165
Throttle valve cutaway #5
Jet Needle R1368H
Jet Needle Clip Position 2nd from top
Slow Jet 42
Air Screw 11/2 turns out.
Mine is a 1993, US model, hope this helps.
royadams
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Re: 1991 KDX 250 Carb specs

Post by royadams »

Good luck keeping your swing arm clean running the factories jetting.lol
Tinie
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Re: 1991 KDX 250 Carb specs

Post by Tinie »

Hi Royadams

What jetting do you recommend for the KDX 250. I live near the coast in South Africa.
royadams
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Re: 1991 KDX 250 Carb specs

Post by royadams »

I live in the south east in the USA close to sea level. Usually it will be 38 to 40 on pilot. 155 to 158 on main. 1 to two leaner needle. And one size leaner slide. And a hotter plug. I ran 38 155 two leaner on needle one leaner on slide. And angk br7es plug. I also had a pipe, reeds and the thinner kx head gasket. If it's all stock start out on the richer side.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

I'm on the Wet Coast in BC, Canada near sea level. Rebuilt engine, pipe, Rad valve and kx head gasket, also had the carb and slide mod by RB Designs.
When I sent my carb to Ron I had installed a 38 PJ and a 158 MJ, as per the mods listed in the KDX 250 forum.
Ron thought that might be a little too lean and recommended 40-42 PJ and 160-165 MJ.
I'm currently running 40PJ and 160MJ, plug is a BR8ES, colour is a light mocha (actually it looks a little too light or am I paranoid).
573
Other than being a little hard to start when cold it's running well, I still need to go thoroughly through the jetting guide, hopefully this weekend.
royadams
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Re: 1991 KDX 250 Carb specs

Post by royadams »

You really need to cut the threads off to see the base.
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Re: 1991 KDX 250 Carb specs

Post by royadams »

Image[/URL] [/img]
Your looking for the black band on the bottom of the insulator. This is an old plug you really want to read a new one. You want around a 2mm wide soot ring. An old plug with color like yours just means it's a decent heat range plug for your current jetting.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

Thanks Roy I was hoping you'd check in. I will cut the threads down tomorrow and check.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

Plug is an NGK br9es 576
royadams
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Re: 1991 KDX 250 Carb specs

Post by royadams »

From a pic it's hard to tell how wide the band is. If it's close to 2mm it's good. If that was a new plug and only has a plug chop on it, I would go back to the br8es plug. The porcelain shoud be almost white.in your prior post you said you have not followed the jetting guide yet. You need to start at the bottom and work your way up. Changes to the pilot curcuit will also effect the main.
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Re: 1991 KDX 250 Carb specs

Post by royadams »

Image[/URL] [/img]
This is what I look for 1 to 2mm ring. Wich is a little on the rich side. I like to run there that way I have a little leway.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

The ring is only about 1mm. The plug was new but not from a plug chop its from after 3-4 heat cycles and a 2hr race (hare scramble).
Going through the jetting guide on Sunday (hopefully).
After the rebuild and carb work I just need to get it up and running and broken in, plus I didn't want to mess with Ron's carb setting until I was sure I had actually put it back together correctly.

Thanks again, and Tinie sorry if I've hi-jacked your post.
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Re: 1991 KDX 250 Carb specs

Post by royadams »

How do you like the rb carb. I was torn between that and the lectron. I went with the lectron only because I ride year round and did not feel like messing with my jets twice a year. If you have 1mm you are good. Perfect jetting will only leave a small hint of a ring. I just dont like to play it that close. Expecially with the crap fuel we have now. As far as cold starts I keep my pilot circuit on the lean side. It starts a little hard when cold, but after a crash it will fire right up.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

I'm the wrong person to ask regarding the carb mod as I can't really compare it to anything and give an acurate assesment. My other two bikes are a 1984 kdx 200 and a 1982 cr 480, both ran well, were maintained and upgraded but the jetting was pretty much left as is. I like how the new(er) 250 feels, nice and crisp, and the mods I did were from the kdx 250 forum and all the info and advice I could find in there (and TT).
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Re: 1991 KDX 250 Carb specs

Post by royadams »

I love my 250, it's such a tractor. With a trials tire and my auto clutch it will lug on up some of the nastiest hills I can find. It's almost like cheating.
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Re: 1991 KDX 250 Carb specs

Post by Asewell »

I have a Rekluse I will be fitting this weekend also and as I buggered up my Hayes brake I have a scooter LHRB to fit as well.
I had a trials tyre on my 200 and loved it, except for the muddy races. I've noticed with my 250 and the carb mods that I can run it so low way past where my 200 would have stalled, but the 250 lugs on. I'm not that fast but aim to always finish, sometimes I'm not even last. :grin:
ArkAngel
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Re: 1991 KDX 250 Carb specs

Post by ArkAngel »

I also live in south Africa and have a 1991 kdx 250.. I'm busy running a 155 main jet and 42 pilot jet with my needle on the 2nd clip from the top.. I was fouling a lot of plugs..

Sent from my SM-G925F using Tapatalk
KDX 200
KDX 250
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