Jetting 101....what's wrong with this picture?

[nostones]

I have been the proud owner of a 99 KTM 250 EXC for about 4 weeks now and I am in the process of fine tuning it to my preferences...I have reached the carb. I would really appreciate some jetting advice and/or recomendations as I am beginning my quest to understand fuel/air mixology.

Here are the specifics -

Location: Atlanta
Plug: BR8EG
Plug tip color: Black & damp, but not saturated.
Spooge Factor: some blowback at silencer/pipe joint, slight drip at tipe of silencer.
Premix: Golden Spectro - 42:1
Needle: Stock N85D, 5th position (highest)
Main: 170
Response: Awesome when cooler (60 & below) throughout entire range of throttle. At 60 & above, bogs at closed to 1/4 throttle position.

Here's what I think I know - the stock clip position for the needle is 3. The stock main is 175. Should I return to the stock settings and work from there? Should I replace the needle? I will be picking up some new jets of varying sizes tomorrow, but if I don't need a new needle, I'll pass on that.

Thanks for any response to this newbie's pursuit of tan ceramic!

 

[Strick]

That is a triple taper stock KTM needle. It may be leaner than the factory. I would drop that needle one clip postion at a time, and work from there.

KTMs do like single taper needles.

 

[Fred T]

A couple tools

This could be the best $19.95 you ever spent
>> http://dirtrider.net/forums3/showthread.php?s=&threadid=32507

Jets for less >> http://www.sudco.com/

A bog at Closed throttle to 1/4 may indicate a pilot jet and air screw adjustment is needed. Usually a bog is an indication of lean mixture and you need to increase the size of the pilot by one. Adjust your air screw for best throttle response after changing the pilot jet.

Different taper needles can open up all kinds of possibilities to manage your mid range throttle performance - you can customize it to what you like - pretty cool really. You can have a "Muddy, snotty, slippery" needle and a "let it rip" needle depending on what the conditions are like.

The there are slide changes. What I don't know is on Katooms what slides they come with and what works with what slides. I'm just a little green bike guy myself.

 

[Strick]

Fred, if you were referring to the JD jetting chart your link didn't work. It might be considered a spam.

nostones my best advice is to learn about the carb. A step by step tuning guide like Canadian Dave has generously authored and posted here on the board for everyone's use. Here is it, and how to navigate to the carb section.

http://justkdx.dirtrider.net/
Go here then click on tech tips, and then click on carb tuning

Good LucK

Oh, and carb tuning can become addictive.

 

[Fred T]

Yeah I was

Originally posted by Strick
Fred, if you were referring to the JD jetting chart your link didn't work. It might be considered a spam.


http://justkdx.dirtrider.net/
Go here then click on tech tips, and then click on carb tuning

Good LucK

Oh, and carb tuning can become addictive.

Oops, didn't think of span, just trying to help, besides I'm not associated iwth JD. But his guide is really helpful none the less.

 

[Rich Rohrich]

The link to JD's jetting guide is fine. Don't worry about it.

BTW it's a good investment.

 

[KTM Mike]

nostones - i cant offer experience with your particular year and model of ktm - but with my 97 300, Stricks and James Deans advice lead to #7 slide and straight taper needle and absolutely PERFECT jetting - clean from just off idle to wide open, smoother "hit" to boot. those two know their jetting!

Fred T - just in case you are lookin for another "snow report" - TO MUCH - got several inches today...more on the way! I have PMS (Parked Motorcycle Syndrome) big time! Do ya know where the snow is gone somewhere within say 8 hours drive? I am desperate!:(

 

[fishhead]

The quick fix is probably to go up one size on your pilot and drop the needle one clip. On my 01 which has a 6.5 slide I use the following:

rich to lean approx
dej-5
dek-5
ddj-3
ddk-3
dej-4
dek-4
cej-4
cek-4
cej-3
cek-3
dgh-4 Just for rooting around fun!
right now at sea level and 45F I am running a 45p 175m ddk-3
In addition to the above needles I use pilot 45 to start and 42 and 48, mains 175-185, use one or 2 steps larger main with the c taper needles. I would start at the rich end on work toward the lean side and go a little past optimum to get a sense of what goes on. Leaner straight sections can be balanced a bit with richer pilot if you get pinging on trailing throttle.

I believe the 99's used a noz_ series needle which is two clips richer than the n85 series needle. I think 98 was the last year for the n85 needle but I may be wrong. If someone can confirm or deny this info it would be good as it would affect the needle selection.

The jetting guide is a great tool jdjetting.com . You can view proposed and existing changes in a graphic format and compare proposed changes. At $40.00 it would be a good tool. At $19.95 it is a gimme. As temps or altitudes change you can plug in the new values and see what affect that has on your jetting. Pretty cool:cool:

The quick fix might be to drop your needle one notch and go up on the pilot one size during cooler weather.( repetition for emphasis)

As a self proscribed jetting junkie I can attest that jetting can be addictive. Have fun!:)

Posting links which does not result in personal gain is not canned meat in my opinion. It's direction to the good stuff!:aj:

 

[Strick]

Fishead, I'm impressed!

I think you have just become my new hero.

That is testing! Thanks for sharing.

I am going to start asking you my 2-stroke jetting questions. ;)

Jet on Fishead :aj: Jet on!

 

[fishhead]

You will be safe Strick since you now run a 4 stroke.

Just to keep it simple I didn't bring up any H, Y, K or S brand needles:eek:

I invested my 401-k on needles since they offered a rate of return far greater than Dow and Co.;) Sudco and Carbparts have good stock right now and UPS is running good so it's a good time to stock the box.

 

[DanS]

My '99 300 exc came with a n85c.

 

[TexKDX]

Guys, be sure and get your references straight when talking about the clip and the needle. This guy says, per my interpretation, that the clip is in the top slot. Therefore, he can't "drop the needle" as some of you are suggesting.

Other than that, carry on and have a nice day!

nostones, the idea that you'd raise the needle when things warm up suggests a need to brush up on the jetting 101s in cdave's tech tips. Warmer air packs less oxygen than cooler air, therefore dictating a need for leaner jetting generally. Your combination sounds lean overall to me, so I'm not sure why it runs OK in cooler weather. A somewhat wet plug tells you little about jetting unless you do high speed shutdowns. Even a lean 2 stroke when putting it around will show a plug like yours. Considering your locale, I doubt you're doing much WFO right now. Good luck,

 

[nostones]

TexKDX,

Thanks for the note. I should learn better jetting lingo, as it appears I may have made some mis-statements. When I picked up the bike, the clip and jetting specs were as listed in my original e-mail. You were right, I couldn't drop the needle any further....for clarification, does the lowest clip position on the needle represent position number 1?? Anyway, I understand the dynamics involved in clip position and warm vs. cold air. I guess I should have stated that I was going to return the settings to stock positions and work out my kinks from there. This past weekend I did go out and buy a few main and pilot jets....

Believe it or not, two weekends ago (when I began this learning curve) I was riding on a natural terrain 3/4 mile mx track with about 1/2 mile woods loop built is, so I was able to get the rpm's up frequently. The bike performs great overall, it's just the start where I was getting the bogging feeling as the temperatures crept into the mid 60's (expecting low-teens tonight...ouch!).

Anyway, thanks everyone for your patience with me. And Tex, I appreciate your help - if you have any other comments, please add them.....

Sean

 

[fishhead]

Mikuni and Kehin refer to the top clip position as the needle sets in the carb as #1, the leanest setting for that needle. #1 Sounds lean to me for winter conditions even with a triple taper needle. I probably wouldn't try a hard plug chop on an unfamiliar bike with a 170 main this time of year. It would be easy enough to drop the clip to #2 to see if that takes care of the bog but it would also be good to know what pilot you are running.

 

[nostones]

Thanks, FH....that clears up some of my own misconceptions. To reset, when I took the carb apart this is what I found -

Main: 170
Pilot: 42
Slide: #6
Air Screws: 2 turns out
Clip position: Leanest (1)

My local KTM dealer set me up with a 40 and 38 pilot. I am going to drop the clip to the 3rd position, install the 40 pilot and adjust the a.s. 1 1/2 turns out....hope for better results. If not, I'll just work from there.

What is your opinoin on those settings to begin my diagnosis?

Thanks again guys...time and effor appreciated!

 

[fishhead]

Depending on temp maybe a 45 or 42 pilot. If you have a bog its usually a lean condition unless it is accompanied by a lot of sputter. Eric Gorr has a tech section on his site that has a "jetting by feel" topic that really helps. Local knowledge of jetting for conditions also helps, I would raise the needle one clip position to start and perhaps turn the a/s in a bit at a time
for jets and needles try SUDCO or Carbparts.com

The small amount of money and time it takes to sort out jetting pays the greatest dividend on modern 2 strokes. Take time Take notes and have fun

Some experimentation will yield a lot of knowledge.