Jetting For The High Plains

What are my Thumper Talk brothers at an altitude of 5,500 feet running for a main jet on thier 03' WR450s ? I've been switching main jets in the 140 to 145 range and still have a full throttle, high-RPM sudden loss of power. The FMF Q pipe prevents a full-on exhaust so that may be part of the problem. The starter and pilot jetting is spot on, as well as the Power Now venturi (low/mid range), so I'm assuming, with all else functioning fine, that the problem is the size of the main jet. :)

I am at 5000 to 6000 ft and I find the 162 main works best for me with the yz pipe. 140-145 seems quite lean.

I'm at 4600-5500ft and I have not yet messed with my jetting. If you get it dialed in would you let me know what works best for you?

My bikes problems are as follows:

1)It bogs for a split second when at low to mid rpm and I wack the throttle to get the frount end up and over say a rut.

2)at 95 to 100 mph WFO it acts like it's hitting the rev limiter but the gray wire has been removed.

3)the head pipe glows like moltan lava all the way to the muffler pipe joint if it idels for even 30 seconds.

Ok before I get all advise of what I should not due,

I know your not suposed to let it idel

I only did the top speed run twice just to see what it would do.

Thanks for any positive advise you or anyone might have.

I'm thinking about ordering custom jet kit offerd on this site. :)

I ride an '02 WR426 with YZ timing. I run a 158 main at 4000-7000' riding elevations. My bike pulls strong all the way to the top. 155 was a bit lean at higher (5500'-7500') elevations, of course late summer temps.


HighPlainsWR, describe your sudden loss of power at full throttle. Is it surging or completely cutting out? Is it WFO or just the upper RPM range? This can help determine if it is the main jet that needs adjusted or the needle. Let us know your complete jetting setup and we can help. :) I'm not sure how much different the jetting would be between a 426 and a 450, but take a look at my signiture to see what I run, both setups work great, but the JD setup is the ultimate.

WR450F_4600FT: Cutting the grey wire does not eliminate the rev limiter, so you probably were hitting it at those speeds with stock gearing.

You are way to lean on the main. On my 450 I run a 165 at 3600 feet and a 158 when I go to the mountains (8500 to 12000). I am runnin stock pipe with gyt insert. Never heats up. Main doesnt effect idle anyway. Just wish my starter was worth a crap. Tim

Hey Highplains Haven't talked to you in a while. Hey I gotta tell you I bought the JD deal and it works great. I got that and it runs great at all elevations.

Hey are you going on any rides any time soon??? Been doing a lot of the Red Cone/Webster to Breck and back over Georgia latley. What about you. Call me if you want the details on the JD thing. My buddy I have been riding with has 01 YZ 426 and was struggling with riding it at elevation not only with the jetting and but also the gearing. So I recomended the JD thing to him and put it on and now he is having a blast. Talk to you later.

I just installed JD jetting with the settings for 6K-9K ft. I ride from 4500 to 10000 ft and the jetting is awesome. I use the red needle with clip in 4th? from top and a 165 main. This setup is slightly lean at 4500 but much better than stock. above 5k it seems spot on.

Yo Wicked and To All,

I knew I could count on my TT brethren. It's a full throttle open situation which happens in third gear on up in the higher rev range. I could be hitting the rev limiter because it's a sudden-loss of all power - a bummer on hill climbs. I have been riding the heck out of the bike and not stopping to tune much and with fall coming it's time to spend some bucks and time in the garage. What's a JD setup (that's a clue as to how long I have been out of TT) ? And what main are you running this fall/winter for Pueblo/Moab elevation ?

Yo Comp 182,

It's so welcome to see a familiar post. What is the "JD" thing ? Since the Revloc install in May, I have put 200 hours on the bike this summer, recently 3 days last weekend at rascally Rabbit Valley. There is the bi-annual Moab/Green River/San Rafeal ride the weekend of October 24th (Game ?) so I got to get this issue fixed. Till then I'm looking for a weekend ride almost anywhere - the super-secret Douglas County area is still open (Game ?). Please give me an update on the "JD" mod and lets ride sometime !!!!!!

At 95-100mph, you're prob'ly hitting the rev-limiter.....the gray wire doesn't disconnect it, it enables the YZ-type ignition advance curve. :)

At Tucson altitudes, I'm running a 162MJ and 48PJ, she loves it!! I also run VP C-12....


Great to see you back! :D The "JD" thing is, James Dean FCR Jetting Kit. You can find it in the TT Store. You can't go wrong with this kit. :)

HighPlains you get the James Dean jetting on this forum. It's like 70 bucks but it comes wit heverything that you need if I remember right. As you might remember I was running the Larryco jetting. Since then I went back to stock air jets and just put in the needle that they recomended. If you remember my header was blue all the way around to the shield with the old jetting not that that means anything, but now it seems to be a lot happier. It does not seem to be any faster than the Larryco but it feels better and safer. The kit will come with jetting for all altitudes with there recomendations that seem to be dead on.

Ok as far as riding this weekend I have to go to South Carolina. But next weekend 11th and 12th I am a riding fool if there is no snow. Let me know?? As far as the 24th I will be in Vegas. AAAAAAAARRRRRRRR. How is it that you seem to be able to ride all this time but everytime I call you your better half seems to think she has something for you to do??? Joking. I think that I have been in that situation a little more than you. Can't live with um and you don't want to take them riding either. Call me if you need more info.

Yo 182...

I'll definetly check out the JD for $70. Iv'e spent three times the price of that on mechanic fees alone trying to get this right. Would you believe the weekend of the 11th my entire in-law family is coming in town and staying at our house ? That is the price I'll pay for straying out to Utah later this month. As a safety measure, I'm keeping the WR Four-Nifty loaded on the truck just in case I need a sanity break. Happy trails :) on your out-of-towners, I'll let you know how the JD worked out.


It's great to be back. To think I spent months and dollars trying to figure this out and all I needed to do was to write a post to my TT brethren to learn about the "JD". I feel stupid. Well heck, I guess I am.... :)

Naw, not stupid, just out of the loop for a while. I know how that goes. Hope things are going well, enjoy the inlaws! :)

Rich Baker thanks on the tip about the rev limiter and cut gray wire thing, I read that the cut removed the rev limiter.

PM me to get that ride or 2 in :)

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