High Altitude WR Jetting Help


I am a newbie and in need of a little help. I have a 1998 WR400 bought used a month ago. I live in Denver and ride in the foot hills. The set up is:

FMF power core 4 pipe

DMC head pipe (I guess that is what it is called)

165 main jet

42 pilot

Needle jet in the #2 slot ( I think it is in the second from the top)

Pilot screw was 4 and 3/8 turns out

Air box lid off

Since I am new to the bike I am thinking about going back to the stock pipe and try to trail ride it that way. The bike seems to run really good. However, it just feel like it needs to really have a lot of RPM’s in order to be in the sweet spot for some of the hills. I have already gone to a 52T rear sprocket to try and correct for this RPM issue. Now I am thinking about going back to a stock pipe. What I do not know is what jetting should I have for each of the setups? Any help would be greatly appreciated. I do have the service manual but it does not talk about jetting for high altitude no less high altitude with a pipe.


if the fuel screw needs to be that far out you need a bigger pilot jet.that main jet is also much to rich.you need to come down to at least a 155.

I ride at 4000ft and higher here in Nevada. I'm using the stock needle, air jets and pilot jets. I've changed the main to a 160 with the needle on #4 clip set. I run a YZ pipe on a WR 426, always have great power and never a problem to start the beast. Maybe around 7000ft., I could have used a 158 main.

Hope that helps. :naughty:

I agree with burned, your pilot screw is out to far. Anything over three turns out and the screw is no longer a factor. I use a 45 pilot and the screw is out 1 1/4 to 1 1/2.

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