High-altitude Jetting results - Colorado

Has anyone tried Klotz CoX-Oc? It is a fuel oxygenating additive that's supposed to contain 37% oxygen. You add one gallon to 5 gals. of gas and you can supposedly use your near sea level jetting at high altitudes like Colorado. It's over $40/gal. but you get 6 gals of fuel and can use it with 2 or 4 strokes. If you're going for a long weekend, once a year, it would be way easier than messing around with jetting changes. One of the bike mags - sorry, don't remember which one, did a product review several months ago. They used it with a 2 stroke and had good success. Check out the Klotz site for more info - www.klotzlube.com. It's under motorcycles and additives.


I too HAD a similar problem at the higher elevations at Rampart with my higher-end. The bike was running more adequately when I was using 42PJ/75PAJ/EKQ#3/155MJ/200MAJ. Try going down on your main by 10 or so...and of course, you could also try clip #2...but like I said, mine was running fine in #3 with a 155MJ.

Havent done anything with the air cut valve. However, the BK mod was done to limit the accel pump squirt duration...which helped substantially! Try that if you havent already done it. Also, although I havent ridden it out there with this setup (yet), the jetting from my post above from this past weekend in Moab couldnt be anything short of awesome up there. Consider the jetting I described above as a good option. Like I said, this weekend I'll be trying the 35PJ/EKN#3 combo at Rampart.

Dougie, I'll email ya about Rampart this weekend. Sat. will probably work best...if we dont get snow (like they say we will).


Larry, I changed to the clip position #2 on the EKQ while still on a 165 main and it ran much better. This was at Rampart. The only problem I have now is that off idle bog. Now if I could just fix that.

Thanks for the help.



Do the BK mod (or the equivalent for a 99 bike)...and that'll significantly help out. Do some searches on it and find out how to do it. Took me only 20 mins. to do the whole thing...and $15...


Kerry, do the mod. Get a wheel collar for an RC car at a hobby shop. It is the next size UP from the 3/32" collar (can't remember the exact size, I through the package away). Slip it on the rod and adjust for only a 3/4 second squirt.

I have no hesitation / bog off idle now. But that is up and down the street just now. Although every now and then it does miss a little at WOF for some reason.

Plus for some reason it won't idle. That is with the idle all the in (slide up). Can't figure that one out.

Thanks for the tips Larry.

I talked to some service techs around town and everyone who had a 426 said to set the needle clip at the stock (3rd) position and start with a 148 main and a 45 pilot jet. I ride from 8000 to 13000 feet here in CO so I thought I would give it a try. I would test it this weekend but the weather is supposed to suck. I'll let you know how it runs as soon as I get a decent ride in.

Wicked Crash,

Yes, every shop person here in town says to go with the larger jetting (45 pilot?). They give me this look when I order things like 35 pilot jets...and 160 main air jets...and especially EKN needles. Funny actually!

Dont go up to the 45 pilot jet. Dougie and I have both tried this and it doesnt work so well. Stay with the 42 pilot jet/75 pilot air jet that's stock in your bike. The main jet sounds OK and the 3rd clip position. Let me do my "final" test this weekend (weather allowing) and I'll throw out a couple of really good/really bad jetting setups for you to go by.

I'd hate for you to try all of these things that I've already tried...although that's learning.


Thanks Larry

Where are you going riding if the weather is nice? Sunday is supposed to be a little nicer than Saturday. If that's the case I might try to go to Woodland Park for a test.


I was hoping to get out tomorrow at Rampart...but given the chance of snow tonight (along with the fact that my friend I'm supposed to pick up at the airport isnt showing up in Denver until 1:45 AM...big delay), I may opt for Sunday. Dont know where yet...but my strong preference is for Rampart.

I'll let you know what we decide on...



Just to let you know, I re-jetted my bike to a 148 mj, 38 pilot jet, and the 5th needle position from the bottom. You were right about the pilot jet, I tried what the techs told me at the dealer and it ran like crap! After I dropped the pj to a 38, I tested it at 8000 ft for just a short 8 mile ride and it runs perfectly so far. I won't know for sure until I take it for a long ride in the mountains though.

another satisfied rider :D:)


4/29 Rampart Range (7K - 9500ft...75F):

38PJ/65PAJ/1.5 turns/EKP#3/150MJ/160MAJ

('01, WR timing, uncorked US exhaust, BK mod)

-Bike started cold first kick every time with choke. Always started first kick warm (no choke or hotstart). Idled well and always returned to idle immediately.

- VERY CRISP AND SNAPPY from 0 - 1/8 throttle. Smooth acceleration upon gradual twist of throttle.

- Great accel from 1/4, 1/2, and 3/4 throttle.

- Excellent high-end performance at max torque and max revs.

- Very little backfiring upon decel. at high revs and 1/4 and 0 throttle.

Same results as obtained two weeks ago in Moab...although better acceleration in mid throttle ranges (it seemed). AWESOME SETUP! When I go to Moab again, I'll probably richen this setup a little (maybe a 160 MJ instead), but overall the best yet!

Didnt get a chance to try the 35PJ combo as promised...too busy helping my friend pick up her bike after countless crashes on the easy trail by Rampart Rd and starting her husband's new YZ250. :) Although, it would be VERY TOUGH to beat the 38PJ setup advertised above...


Just thought I would let you all know, I went for a 40 mile ride on Sunday at Woodland Park (around 9000 to 10000 feet)and my WR ran perfectly. No loss of power anywhere, a few backfires while decelerating down hills, and no bogging! I'm pleased with the results so it's time to stop messing with the carb and time to move on to more accessories! Thanks for everyone's advice in previous posts.

Larry and Wicked,

Does this syptom sound familier? Bike starts easy, need choke for a cold start and hot start for hots. I get a stumble/rumble/valvefloat/miss, at about 1/2 throttle. When I roll the throttle into the last 1/3 of the throttle, This bike will break traction, roost like a big dog, try to pull the front wheel up, launch like a rocket.

All this while I still feel like i have a stumble.

This bike has standard air jets. stock needle, needle has been raised one position. 45PJ and 158MJ. I am betting on a different needle, or raising the one I have another position. Or would you suggest I copy your jetting specks for this area?? I just rode this morning so I havn'nt had the chance to pull the plug yet.

Let me know what you guys think.



I notice you haven't cut the grey wire. It probably needs jetting too but this may be worthwhile first.

Good luck,



That sounds pretty much like my bike when I first got it. I would suggest you try the settings that I or Larry used, they are pretty similar. It may sound like a big drop for your main jet but try a 148, I went from a 160 to the 148. Also drop your pilot jet, I went from the stock 42 to a 45 that didn't work so I dropped it to a 38. It sounds like you raised the clip to the 5th position, if so that should work fine. All bikes are different though but this should get you in the ballpark. Good luck, let me know how it turns out. :)

wicked crash is right. drop the MJ and it will disappear. if it doesn't drop the needle once then twice. do the PJ last and again he's got it going the right way.


Mark, Wicked, Taffy;

I am assuming that you feel like I am running rich? When I pull the plug, What if it comes out lean? Should I still go ahead and make the changes? Mark, I have cut the grey wire, but have not added it to my sig yet (sorry). I really want to thank you guys for your help. I am trying to learn enough about this process to do the other bikes in my stable.

Once again, Thank you, Thank you, Thank you!!!


Racemile (funny name! :) ,

It's hard to just pull the plug to determine if your entire bike is rich or lean...as throughout the throttle ranges you may be both! You'd have to idle the bike for a little while and kill the engine, run at 1/2 throttle around the neighborhood and kill the engine, run at FT...etc. Dont put too much stock into the "checking the plug" thing as the bike's running at each throttle position should tell you what you need (lean, rich, or just fine).

Next steps are up to you. If you're the type of person that wants to experiment on his own, then start playing around with different changes (make only one at a time and check the results), read up on the effects of the different jets (link to good starter article included above in first post), and potentially even ask James Dean for his jetting spreadsheet. If you're not and you'd like to get your bike running much better without spending a lot of time, then just copy either of our jetting specs and run with it! I personally am somewhere in the middle...and have done some playing around.

Good luck...and let us know if you need any other help...like with part numbers, etc.

See ya!

Larry, Wicked, Taffy;

I replaced the MJ. I went from a 158 to a 148. I replaced the PJ. I went from 45 to a 38. The stock needle is still raised one position.

Any guess at the results? I did the around the block test. The stumble/stutter has moved up the throttle to start at about 1/4 throttle. The bike started fine and idled fine on the choke and off the choke. The revs returned to idle quickly and didnt hang or anything else.

If I blip the throttle I could kill the bike. Would start with the hot button, but would quickly die if you didnt get it off fast.

If I am understanding things correctly this would mean that the bike is running lean at this point. This should be adjusted, as Taffy stated, by lowering the stock needle 1-2 positions. All other jets in the bike are stock.

Let me know what you think.

Thanks in advance,


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