yz jetting

6 replies to this topic
  • ncmountainman

Posted September 20, 2004 - 03:50 PM


i'm running a yz airbox on my 04 wr 450 and since install it seems like its a little lean on the mid-top. i'm wondering what the yz's run for jetting with a simaler set up as mine. i've cut the gray wire so the mapping is now yz,i guess the only difference would be the cams. the pilot circuit is fine, i'm thinkin maybe up to a 170 mj from 165? my specs are listed below and elev.is 2000 - 2500 ft avg.temp is around 65 right now. :cry: :cry:

  • WR426madness

Posted September 20, 2004 - 04:30 PM


170 is probably a little steep, how does your plug look?
Try a 168 first if your plug is really white.

main jets
try this link good prices on jets, it is a snowmobile site but the hex Keihine main jets are the same

  • sjwr450

Posted September 20, 2004 - 08:19 PM


When I did that to mine, I went and bought the two air jets (don't remember what they are called) that go in the carb where the Airbox connects, check your manual. I also ran the JD red needle.

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  • ovrrdrive

Posted September 21, 2004 - 12:56 AM


I'm running a 168 in my unmodded YZ, but I'm basically at sea level or just a few hundred feet above. At your altitude you may very well be a little leaner than me.

The best advice is try a 170 and see how it runs. It's like a 10 minute job to change it.

Btw, I got my jets from the TT store. Just call them up to make sure you get the right stuff.

  • ncmountainman

Posted September 21, 2004 - 10:29 AM


just happened to find a 170mj(think it came with the bike)threw it in and holy crap! i didn't think it would make that much difference,but i guess between more airflow with the yz box and it starting to cool down a little it worked out. thanx for the help. :cry:

  • Fastest1

Posted September 21, 2004 - 12:53 PM


Try a 168 also, the subtle differences in size can make a big difference in performance.

  • ncmountainman

Posted September 22, 2004 - 06:29 AM


thanx,i will pick up a 168 to try in the spring,but now with cooler temps setting in i will just leave the 170(it is as close to perfect as its ever been)man it just comes alive now mid-top no hesitation,in fact during my remodel i was thinking about putting in YZ cams to wake up the top end but the airbox and proper jetting is making me think i should leave well enough alone. right now its almost out of control but very tractable,i think it might not hook up as well with the yz cams,what do you think? i ride woods and will be racing an occasional harescrambles(mostly tight woods mixed up with a little MX) :cry:

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