1991 KDX 250 Jetting question

[43Duc748]

My KDX250 is running too rich and I'm getting black gunk leaking at the seals. The bike has an FMF fatty pipe and turbine power-core silencer and a K&N filter. The previous owner said he never changed the jetting and has been running it fine. I think he just overlooked the leaness and ran with it.

I've never re-jetted a carb before, but it seems pretty easy. I did a good search of the forums and found different suggestions for jetting:

1) 38/158 , R1367H needle 3rd clip from top, #6 slide

2) 42/165 main, 2nd clip

3) 38/155-158 jetting #6 slide and 1367 needle

As you can see, there are various combinations of clip, needle, slide and jetting. I live near sea level and ride in the deserts of Southern California. Can anyone offer some decent asvice or what I have? I'm pretty much an idiot at this, but I am having fun learning!

 

[43Duc748]

Bump. I'm hoping to re-jet my bike this week. According to the Kawasaki parts list, the only main jets available are 160, 162, 165, 168 and 170. If that's the case, then the only option is the 42/165. (isn't 42/165 the stock setting?) Any help is greatly appreciated - I want to ride!

 

[dirt bike dave]

It's been a few year since I sold mine, but I know I used a 38 pilot. The stock jetting is ridiculously rich on this bike and very poorly done by Kawasaki. I think used 158 on the main jet, but I usually ran at about 4,000 feet. The stock slide cutaway is also not enough and too rich for low rpm running. You can grind 1mm off the bottom of the slide or buy a slide with 1mm more cutaway. For sea level I would try the 160 main.

Can't remember which needle I used, but I think it was leaner (higher #) than stock. Try moving your needle clip to the top groove if you have the stock needle.

You can also safely run a hotter BR7ES plug if you are in the tight woods. I would stick with a BR8ES for more open riding.

Another cheap mod for your bike is to use a thin head gasket from an '88 KX250 for more compression. It will still run fine on pump premium and have better low end power.

The FMF pipe and an aftermarket silencer (you can modify one from a KDX200 to fit) will save a lot of weight, smooth the low/mid hit and give more rev on top.

 

[Green Hornet]

Put the bike jets back to original specs. Then adjust jetting according to the manufact recommendations-IE any mods that have an effect on air fuel ratio. Temps & altitude have an effect also. Change on circut at a time. Go to the tech page in DRn & look for carb tuning. It has a graph & instructions that will give you an approximate. Good luck :ride:

 

[43Duc748]

Okay, thanks for the input. The jets on it are stock. The pipe has an FMF pipe and FMF silencer. It's running rich... I've got black goo coming out of the pipe joints. I did an extensive search of jetting options for the KDX250 of my vintage. I guess my question is, one of the popular recommendations is to use a 155 main jet, however, the Kawasaki parts list of options for my bike does not include that size. the lowest they go is 160. Are there 155 main jets that will work in my bike from other models? I want to try 38 / 155, but no dice so far...

 

[Green Hornet]

Look what the manufacter recommends for the pipe also try a Hotter plug. Go one jet at a time and see waht the results are. Just dont drop several sizes at one shot. Also is it spewing on idle? The vintage bikes are knwon to be super rich on the pilot. My 85 KDX200 was super rich, but I dropped the piolt one andwen to a hotter plug at that time and it worked great

 

[dirt bike dave]

The #155 or #158 main jets from a similar vintage KDX200 will work. The bike is so grossly rich with stock jetting that going one size at a time is just going to waste time and cost $.

 

[43Duc748]

Today I changed the jets to 38/155. I didn't change the needle since my local shop didn't have them in stock. Not too mention they were about 15 bucks higher than Ron Ayers. Anyway, the bike idled much better and seemed much snappier when I took it out for a test ride.

By the way, for all you KDX250 owners, I put togther a quick web-page compiling the different KDX250 tips I've gotten from DRN. I read a ton of posts, so I thought I'd compile them for others:

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

 

[dirt bike dave]

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

To The Top for the newer KDX250 owners. Be sure check out the KDX tips tab at the bottom right of the page. Big thanks to Chris for summarizing all that stuff!

 

[43Duc748]

Thanks for the props, Dave. If anybody has anything to add to my tips compilation page, just send it my way and I'll add it in there. As the years go by, the resources for KDX250's get thinner. I'll keep the page as long as I have my 250 which will probably be a while... next toy - motor-home!

 

[43Duc748]

Still having spooge!!!!!

Okay, I am stumped on the jetting for my bike. My jetting is as follows:

38/155 jets
1367 needle, 3rd clip from top
stock slide (#7 I think)
Boyesen Power reeds
BR8ES plug
air screw 1.5 turns out.

Bike seems to run good, but spooges really bad. It's all over the swingarm and coming out the end of the pipe. I had previously flushed out the pipe and re-packed the exhaust.

I'm getting a bit frustrated now! I'm running my bike in SoCal in the high desert (not sure on the elevation, but probably around 1000 to 3000 feet. Temps are about the 80's. The bike idles pretty good.

Any advice is greatly appreciated!

 

[dirt bike dave]

Chris - I can't remember which slide # is stock, but the preferred slide has 1 mm more cutaway than stock. Or you can grind about 1 mm off the bottom of the stock slide (scribe a line then grind up to it). If grinding your own, you could experiment with less than 1 mm. Make sure your existing slide is stock cutaway before grinding. The previous owner may already have put in the right slide.

FWIW, some fuels and oils spooge more than others, even with good jetting. Also, with a torquey trail bike like the KDX250, you tend not to flog it at high rpm. Low rpm may result in more spooge than screaming the thing.

Racing oils designed for superior high temp protection may spooge more in a trail application than other, more trail oriented oils (I use Maxima Super M).

Pesonally, I would experiment with the slide, different oils and fuels (change stations if running pump premium).

Finally, it is much more improtant that the bike runs well than whether or not it spooges. On a trail bike, you probably don't want to be jetted to the razor's edge, as conditions can vary dramatically on a long ride. And WD-40 is pretty good at removing the spooge.

 

[Jim Crenca]

Two different issues here IMO.
Spooge can be the result of rich jetting, but could also be the oil.
Many on DRN are happy with either Mobil MX 2T synthetic or Yamalube semi-synthetic.
I would try one of these oils and jet the bike properly (good thread in archives on plug color).
There will always be some spooge; is it leaking at the pipe to silencer connection or out the end of the silencer?

 

[43Duc748]

The spooge is coming out at the cylinder, at the pipe junction, and at the very end of the tail pipe there is residual. My riding buddy says my bike smokes a lot, but I don't see it when it's idling and revving. I ride mostly trails, a lot of 2nd gear climbs w/ wfo as well as 3rd and 4th gear crusing.

I'm runnin Yamalube 2R at 40:1 w/ regular pump gas (87 octane). I briefly switched to Bel-Ray MC1 but that spooged as much, so I cleaned and re-packed and went back to Yamalube.

As for grinding the slide, do you just grind it even across the bottom of the slide? Mine's not been ground by the previous owner. I'm hesitant to do that 'cuz I don't want to screw it up, but if it will help, then I'll go for it.

I have read a lot about setting up the jetting the correct way, ie plug chops, but I live so far from a riding area that I don't have any way to do plug chops, so I have to make adjustments and then go out and ride and get a seat of the pants feel for it. I honestly didn't feel any difference in the bike when I added the 1367 needle, or the Boyesen reeds.

I'm almost to the point of not caring, but it does get old having to clean that spooge all the time, as well as re-packing more often than I'd like!

Thanks for the help guys!
-chris

 

[dirt bike dave]

Chris - Switch to pump premium, even though its only 91 octane in CA. The gas you use can absolutely play a roll in how much spoooge is generated.

My buddy ground his slide on his '92, but my '91 already had the different slide with 1mm more cutaway when I bought it. I know the bottom of the slide is angled, but I think he took about 1mm off evenly.

Plug chops are way over-rated.

http://www.eric-gorr.com/techarticles/carbtuning.html is one of Eric Gorr's articles. Skip about 2/3 of the way down to the ride and jetting by feel section. It involves doing circles at various throttle settings and seeing how the engine responds.