Re-visit High Altitude Jetting

I have a 99 WR400 and trying to prepare for a trip to Colorado (Ouray & Crested Butte). I've searched the archives, but can't find info on the 99 and/or don't understand. Can someone give me simple advice on what I need to do to get my bike to run decently out there. I have a stock exhaust with aftermarket baffle, no airbox lid, cut greywire.

I'm not very mechanical - Can someone also simply explain what the different carb components do - example: fuel air screw - 0 - 1/2 throttle. etc.

Thanks or any helpful advice.


Originally posted by mikem:

I'm not very mechanical - Can someone also simply explain what the different carb components do - example: fuel air screw - 0 - 1/2 throttle. etc.

Thanks or any helpful advice.


Short story:

0-1/8 - pilot

1/8-3/4 - needle

3/4-4/4 - main

The fuel screw acts as a fine tuning mech for the pilot. There is quite a bit of overlap between each of the jets but the above is a good reference. Since you're coming from approximately sea level to 9K' ASL (and above, depending on where you ride in Ouray) you'll need to be much leaner on all your jetting. I think a good thumbnail test is about 20% leaner across the board. I can't offer any numbers for jets as I don't ride a similar bike.

You might be able to get some help from:


PS, Colorado is as dry as a tinderbox right now. Be SURE you have your spark arrestor as the FS doesn't have much of a sense of humor these days.

Check out "High Altitude Jetting - CO"...a thread with my jetting results over the past year. Right now, the best Ive found to work at those high altitudes is:

38PJ/65PAJ(S)/1.5 turns/EKQ#2/150MJ/160MAJ.

(WR timed, stock uncorked exhaust, BK mod.)

Although, admittedly, it's not perfect. Please post your results if you try something a bit different...

Hope you have a great time! Ouray is an awesome place...


Thanks for the advice.


I have a 99 WR400 - I have riden it the last two years in Crested Butte and Ouray. The only changes that were made were a leaner main jet. It runs great in the high altitude. I'll be out there again the begining of September.

Enjoy your ride


Mike Kelly: What main jet size were you running.

We changed our main jets to 158 or 155 last year (can't remember and lost the piece of paper) The bike seemed lean in the town (Crested Butte) and ran good at 9500 to 11,500 and then became Rich at 12,000 or so. Our bikes were very hard to start and we now suspect rich at the low end of throttle - Pilot jet?- because the pilot jet was stock.

Any other thoughts or advice from others.

What a great part of the country!!

Mike Kelley are you doing an orginized ride out there or just riding for fun??

Hey guys

Unfortunatly my bike is in Colorado right now, but I have a call in to the gentleman who did the jetting. Will advise as soon as I here.

I'm riding an organized ride. ( Colorado 500)

Have fun


Mike thats what I was wondering. I will be there as well as Merf. We will have to try to hook up for a beer or something along the way.

Mike, see ya at Wally's!


Hey guys:

I don't want to beat the dead horse on this subject, but I'm still a little confused. Looks like the advice is to run a 150 main jet out there. Last year I ran a 158 and it ran too lean, especially in town. We messed with the needle clip setting and finally had it acceptable. It ran lean down low in Crested butte and Rich at the tops of mountains. Could the difference of advice/recommendation be that I have a 99/400 with stock pipes vs. other with 426's and aftermarket pipes? More advice would be helpful.

PS: I'm coming out with a group of friends (19 of us from Georgia). We will be in Ouray 8/1 - 8/4 And Crested Butte 8/4 - 8/8. Of course we will do our part to be good ambassadors for the sport and spread good cheer in the local saloons and hottubs! :)


I've always ran a 158/160 in colorado. I used to do Pikes Peak ,Cripple Creek and 4 Corners every year with a 158 and 1/4 turn on the FS with no problems.

Bonzai :)


Ive ride those places all of the time (given that I live out here!)...nice choices!

I think it's all a matter of personal choice here in what people believe is their best setup. All I can say is that at altitudes of 9500 ft and up, I run the following with good fortunes:


'01 WR...lid off, stock uncorked exhaust, BK mod.

I didnt really notice that the bike was anywhere close to overly-lean at 9500 ft...and the bike ran awesome on top of the mountain passes (13K+ ft.). I guess I'd rather run a bit leaner in town where I'm taking it easy than having plug fouling problems on top of an exposed mountain...but that's just me. I think you'll find that there's quite a big difference in your bike's performance between the two extremes (9500 vs. 13K) jet where you're comfortable and go with it.

Good luck and have fun!


Oh, forgot to buddy rides the same bike as I...with the same mods...and isnt into jetting (for some reason...probably just laziness! LOL). He's been running the following with OK success...and has never fouled a plug doing it:


You'll notice that just about all of that is stock on an '01...except the MJ and clip position. Just another way to go...

[ July 25, 2002: Message edited by: LarryCO ]

Thanks Yamakazi - I saw MXTuner last night - he knows his stuff. Dirtbike doctor!! He lowered my suspension 1 inch, moved bars up, added a steering dampner and put on the IMS tank/moose seat combination. The bike handles much better for me. I feel much more confident on it for the steeps in Colorado.

Thanks LarryCo. I appreciate all the advice. You do live in a great part of the country and we look forward to visiting there. Here we talk all year of our ride in Colorado!


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