OK, My Turn You Jetting Gods

17 replies to this topic
  • Dougie

Posted September 08, 2001 - 01:57 PM


Just curious, if you jetting brainiacs lived in the mile high altitude of Denver, what would you use as a starting point on your hypothetically owned '99 YZ timed WR with FMF header and pipe with all the free mods.

The reason I ask is that I've never felt I've been right on. But it runs and doesn't foul plugs. There is some minor backfiring in higher gears and speeds but usually only at higher altitudes than Denver. I usually just adjust the fuel (or is it air) screw to get rid of it. There just isn't the get up and go with the throttle twist at any alt.

I haven't touched it in about a year and a half. I ride it the same here in Denver or in the mountains. Just don't have the time to mess with the carb anymore (new parent). But I am tearing the bike down for mntc before I go to Moab and figured while I have easy access to the carb, maybe I will do some tinkering. If it is OK with you, I don't want to tell you what I have in there now (mainly because I don't know yet, forgot to write it all down). I was just wondering what you would start with? (Did I just take the long way around to ask a simple question?)

Thanks guys, Doug

  • James_Dean

Posted September 08, 2001 - 04:11 PM


Hick? would you give some input here?

Something like EKQ#3, #45 pilot, and a #165?

  • Thumper33

Posted September 08, 2001 - 06:28 PM


I'm not trying to steel your post, but I figured we're both in the same boat here so maybe I could jump in at the same time.

I just got my 2000 WR400 and I live in Littleton not too far away from Parker. I have no idea what's in there either, and I have yet to mess with anything (mainly cause I don't know what it all does, or even how to read performance to see what I need to do). Here are my simptoms...

1.) I can't go at a slow constant speed without the bike wanting to buck a bit, it's either accelerate or don't. By reading another post, It sounds like I might be running rich ???

2.) mild backfiring when decelerating from high speeds.

Here's what I'm afraid of... I don't know how sensitive to altitude and temperature this bike really is, and I don't know what altitude I'm really riding at. I know there's an adjustment on the side of the engine for mixture, but I don't know which way is which, or how much to turn it.

I'm not a mechanical idiot, in fact I know a lot about engines and such, but I'm used to fuel injection which does the magic for me. About time I learned this I suppose hey?

[This message has been edited by Thumper33 (edited September 08, 2001).]

  • Stefe9999

Posted September 08, 2001 - 07:07 PM


Hey guys,
I live up in Northern CO. My new 426 does the same, rough running at low constant rpm and great everywhere else. I just lowered the needle by one position, this fixed the problem for a guy called Northernryder. I will ride it tomorrow and let you know how it affected the problem.

My bike has a #158 main jet and the DQR needle at clip position 3. I don't know what the other jets are yet.

  • Dougie

Posted September 09, 2001 - 03:40 PM


OK, I think I'm running the following:

Needle: DVP (possibly DVR) 3rd clip
Main: 172
Pilot: 48
Screw: 1 1/2 to 1 3/4 out

  • Stefe9999

Posted September 09, 2001 - 03:45 PM


Lowering my needle did not help the rough running problem. I did characterize it a little better, it happens really at a midrange type of rpm.

I've explained the problem over on another thread related to jetting. Keep an eye open there to see if I get any response.

  • Hick

Posted September 09, 2001 - 05:27 PM


Originally posted by James Dean:
Hick? would you give some input here?

Something like EKQ#3, #45 pilot, and a #165?

Here is what worked in my ’01 YZ up at Rampart Range in July:

EKQ # 3 (this is the stock ’00 YZ needle, PN: 5JG-14916-ER)
# 38

Here is what I run at 4k feet:

EJP #3

I also have an adjustable PAJ screw, set somewhere around # 85, no MAJ, and a modified accelerator pump on my ’01 YZ w/ a Q series silencer.

Since you have the 400 and the slant carb this may not mean as much to you, but I think what JD suggests would be a great starting point given that the 400 seems to want a larger pilot.

Guys, I wouldn’t run the D taper needle unless you put the stock exhaust and airbox lid back on, or at least until you’ve tried the E (YZ) taper. When you think about it this is the only significant jetting difference between the two models, and the only significant engine difference is the exhaust, airbox and cam timing. So it stands to reason a free-breathing WR will prefer YZ jetting. In my (limited) experience changing the main jet a size or two is hardly noticeable on these bikes.

Hope this helps.

  • James_Dean

Posted September 09, 2001 - 07:55 PM


Smaller pilot jets than I thought, how many turns out on the pilot screw?

Thanks Hick


  • Hick

Posted September 10, 2001 - 09:10 PM


Originally posted by James Dean:
Smaller pilot jets than I thought, how many turns out on the pilot screw?

Thanks Hick


Sorry ‘bout that, I was around 1.5 in both cases (Rampart ~ 8k and down here at ~4k). As for the smaller pilot, I have consistently found that the 426, both the ’00 and ’01, really liked a 40 pilot in the summer where I ride, high and hot.

I bought the 38 to try at Rampart after reading about a Denver rider on the YZ side whose dealer put a 38 in his bike. That seemed awfully small, but it was much better than the 40 at Rampart, my bike was almost unrideable with the stock 42 in there at that elevation, but I’ll remind all that the Q silencer I’m running is likely richening things up slightly, my buddies ’01 YZ wasn’t too bad with a 40 pilot and E-
Series silencer (only bought one 38 pilot) but still a bit rich.

My winter jetting down here (up here?) at 4k, based on experience with my ’00, will be a 42 pilot and maybe a richer clip position (never tried a J needle in the ’00).

My ’01 with the Q silencer, BTW, based a few VERY unscientific back-to-back tests in my garage and driveway, is only slightly louder than a stock 520 EXC. Really.

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  • Dougie

Posted September 19, 2001 - 02:13 PM


Wow! How can I be so far off and it still run?

So I'm hearing I should possibly run EKQ #3, #38 and 160 in the Denver altitude 6000 to 9000 feet. Is this correct?

I noticed Hick has a 426. Would the jetting be the same for a '99 400?

I am going to Moab Oct 5th. It is around 4000 feet if I am not mistaken. Should I try EJP #3, #40 and 162?

One more question, what am I missing in power by running a 48 pilot, 172 main and a DVR #3? What differences should I look for or notice when I go to a EKQ and leaner jetting?

Thanks guys, Doug

  • Bill

Posted September 19, 2001 - 02:44 PM



Read the jetting in my signature and back off on the main and pilot jets. Rememeber I'm at much lower elevations than you.

Also with the pipe and YZ timing, you'll benefit greatly from going to an "E" series needle.

I would guess you should be in the 170-175 MJ, 42-45PJ and EKP #4-6.

The jetting for our 98/99's is richer than the later model bikes.

Your bike may be running ok but, if you run it leaner, you'll find more power.


99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, de-octopussed (Thanks Clark) EKP #4, 50PJ, 175MJ, 100PAJ and 65 SJ at 500-1000' Thanks James Dean!

  • Hick

Posted September 19, 2001 - 03:20 PM


EKP vs. EKQ, latter is just slightly leaner just off the pilot. The ’00 YZ actually came stock with an EKR, one more size leaner (and too lean for most places).

Bill thinks clip # 4, JD says try # 3, I would also say #3 in Denver and when you go to Moab, I’ll take a wild guess that it is warmer there than where you ride normally and that can make as much of a difference as a thousand feet or so (or more, maybe we should figure this out. Where is that altitude density calculator website?).

On my YZ, going from 4,500k to 8k, same temp., is worth at least one clip position and one pilot size. So if Bill’s bike runs good at 0-1,000 ft. or so then, going way out on a limb, I’ll say that I think EKQ #3, a 45 pilot, and a 170 main would be a good place to start, and should be better than what you are running now.

Since you are currently running a D taper needle I can only guess at the difference you will feel, being a YZ owner, but clearly that is the most significant change among all the suggestions, but it is actually richer, almost everywhere. Noting your mods listed above, with the E needle you will now be riding a WR with a YZ400 engine, so that is what it should feel like. :) So many guys have put the YZ taper in their WR, and I don’t think I can recall even one who went back, esp. if they had exhausts, no lid, blah, blah, blah.

The leaner pilot I would think would make it easier to start and provide crisper throttle response and better “cruising” performance (low rpm, low throttle).

Hope this helps.

  • James_Dean

Posted September 19, 2001 - 05:35 PM


I think the discussion has gone full circle and my first jetting suggestion was pretty good.

Dougie, it will give you the "get up and go with the throttle twist" the bike has been missing.

  • Hick

Posted September 19, 2001 - 06:52 PM


Originally posted by James Dean:
I think the discussion has gone full circle and my first jetting suggestion was pretty good.


JD, you are the man when it comes to jetting, and everybody knows it. I THOUGHT I knew how to jet a bike until I ran into you. I’m sure I ain’t the only one who can say that either.

You could probably make my chainsaw absolutely rip! It’s running a little snotty:

Poulan 380
6k ft. elev +
stock exhaust
stock jetting
1mm dia. hole in the exhaust pipe



  • Dougie

Posted September 20, 2001 - 05:10 AM


Thanks guys, I truly appreciate your help and input. I'll get a couple of E series needles and start from JD's suggestions. I'll just experiment in the next few months. I am starting a Hare Scramble series in late Oct. so that will be my testing ground.

  • Thumper33

Posted September 21, 2001 - 09:28 PM


Hey Dougie,

I'm just south of park meadows mall. You can't be more than 10 miles from me. We'll have to hook up some time.

I'm really hesitant to go to YZ timing because I hate messing with jetting as it is. Maybe it's because I don't have a nack for it yet, but I'm afraid to mess with it. I'll see how yours works out and maybe follow your footsteps when you get it worked out.

Email me and we'll hook up some time...


  • Dougie

Posted September 22, 2001 - 05:25 AM


Sure thing T-33. You are correct, I am 5 miles from PMM. I will definately email you soon. I doubt I will be riding around here until after my Moab trip Oct. 5th. My bike is pretty much torn apart right now for Moab mntc. I hope to get it back together this Sun (but not in time for the Poker Run at Rampart unfortunately). If I do get it back, I may go for a testing ride next Sunday at Rampart just to make sure I put back together correctly. I'll email you if I go. Doug

  • Stefe9999

Posted September 22, 2001 - 04:28 PM


Dougie and 33,
I'm an hour from PMM, I'd like to meet you guys too. Friends and I will be getting to Rampart pretty soon. I might come down by myself if you guys are going sometime soon.

I have made progress on the jetting front. I've found that with my Euro pipe, my current jetting is pretty good. I just put the pilot screw out to 1.25 turns from 7/8, and popping is better. My jetting is off with my free flowing US pipe, so per the replies I've gotten here and just lots of reading, I now have a EKQ on order (got it for $17.99). Maybe with this my bike will run good with the US pipe.

01 WR426, uncorked stock pipe, DQR POS#3, #158 Main.


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