Jetting for Altitude

I just moved back to Reno, NV and need to rejet my '00 WR400. I am having difficulty starting the beast when it is hot. I am also getting some mild backfiring with my current set-up (when slowing down from higher speeds).

Any of you WR experts have any recommendations for main jet, needle, clip position? Unfortunately I do not know what is currently in my bike but I can say that under my current settings I fouled a brand new plug on its 1st time out. However it was not wet - it was bone dry and covered with black carbon.

Any help, advise, or starting point would be great. I already took my bike into the local dealer to have them tune-up, adjust valves, and re-jet but SURPRISE still having difficulties.

Sounds lean..........

Check your jetting settings, and report back with them, along with riding elevation and temps. Cannot do anything till we know where your at :).


Dodger :D :D

If you have it jetted right somewhere you can use my Excel jetting spreadsheet to adjust for temperature and altitude. Download it at:

However, the dry sooty fouled plug you describe can be due to poor fuel. Oxy (ethanol) fuel mandated here in the winter wreaks havoc on the YZFs. I had a constant fouling problem due to it. Try a good quality race gas and see if the problem goes away. Don't blow this off (I did for a while, gas is gas right?) Its an easy thing to try.

Check your private messages I tried to send you one but I don't know if it worked or not.

Anyway, if it didn't, my bike is jetted pretty close to good for the Reno area and my set-up. My bike is probably a tad rich, plug gets a bit black, never wet, never fowled, and starts first kick hot or cold.

Main = 170

Pilot = 48 (thinking about changing it to a 45)

Needle = stock (OBDSS?) in clip position 3. (May change to a leaner needle)

Fuel Screw is about 2 turns out.

Give it a try, hopefully this is a good starting point for ya.

This weekend I'm gonna give VP's Ultimate 4 (96 octane) gas a try too. Guess it's supposed to lean the bike a little cuz it burns alot cleaner than pump gas & supposed to give a noticable performance gain too.

My buddies and I are always looking for new guys to ride with and if you'd like to join us sometime your more than welcome. I'm old & slow and usually I'm at the back of the pack. The rest of the guys vary from slow novices (like me) to fast amature riders, and an expert or two once in a while.

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