Need 2002 YZ jetting specs!



9 replies to this topic
  • BigDesto

Posted May 17, 2002 - 10:26 AM

#1

Putting a yz muffler on my Wr426,I need to know what the stock jetting is on the yz426 02'. I want to start with that set up 1st.Already yz timed,grey&blue wire unplugged.Whatz needle also?
Thanx,Mike :)

  • Hick

Posted May 20, 2002 - 06:39 AM

#2

Originally posted by BigDesto:
Putting a yz muffler on my Wr426,I need to know what the stock jetting is on the yz426 02'. I want to start with that set up 1st.Already yz timed,grey&blue wire unplugged.Whatz needle also?
Thanx,Mike :)


Should be EJP #4, 162 main, 42 pilot.

The needle is far and away the biggest difference, the main and pilot are only one size different I believe, but the needle has a different taper, and that makes a large difference thoroughout the throttle range.

Hope this helps.

  • BigDesto

Posted May 20, 2002 - 07:50 AM

#3

Thanx,Hick

My bike runs pretty good right now,Everything is stock wr jetting,165-45. The yz is 162-42 and a EJP, i have the jets, just need to get the needle.
Since i'm running yz timing,yz muffler i want to throw in all the yz specs.Is the YZ needle thinner or fatter(richer-leaner)?

  • yznvegas

Posted May 20, 2002 - 08:15 AM

#4

The stock jetting is very rarely applicable to the application because of environmental issues such as heat, altitude, and humidity. Unless you are in so. cal. the stock yz jetting wouldn't apply anyway. I guess it would be a good place to start but if you are up at a high elevation you might want to start a little leaner than stock, just my thoughts.

  • Hick

Posted May 20, 2002 - 11:23 AM

#5

There are some guys on 400s, particularly the WR side of this board, who are running D taper needles and are happy. I believe YZ 400s came stock with a D taper, the 426 w/ an E.

I would say for the 426 the E taper is better for just about any elevation as soon as you uncork and uncover the WR.

To answer your question Desto, the YZ needle is both thinner and fatter. I think a good way to explain the difference that the E taper makes vs. the D is that it richens the rate of change relative to throttle position, that is why it affects a wide range of throttle position. Most who try an E taper in a free-breathing WR note the more aggressive mid range response to throttle. The affect is the same in a KTM w/ an aftermarket exhaust, BTW.

Adjusting for altitude then is left to the needle straight, clip, pilot and main. In my experience the E taper works well, in uncorked/uncovered WRs and YZs, at elevations up to 8k ft.

Here is what I run at 4k ft.:

EKQ #3
160
40
~85 PAJ
MAJ removed
1.5 turns out on idle mix

This works well for me. I also have limited the accelerator pump to 1mm of stroke.

Hope this helps.

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  • BigDesto

Posted May 20, 2002 - 12:07 PM

#6

YZnVegas- I am in so-cal, canyon country is near Magic Mountain if you know where that is? I just want to start with the yz specs first and then take it from there.Right now the bike rides fine,with the stock Wr jetting.Just want to see if it can any chrispier?

Hick- the stock needle on a 02 YZ426 is ejp correct?
I want to start out with that one first and then go from there - if need be.

Thanx,Mike :)

  • Shawn_Mc

Posted May 20, 2002 - 12:22 PM

#7

Your biggest deal with going to the YZ specs is, your cam timing is what will require the fatter jetting of the YZ, not just the pipe.

  • BigDesto

Posted May 21, 2002 - 05:51 AM

#8

Shawn, yz jetting is leaner than the wr. I've yz timed my bike and got the yz exhaust,why would you think that i would need to go richer? :)

  • Hick

Posted May 21, 2002 - 09:01 PM

#9

Originally posted by Shawn Mc:
Your biggest deal with going to the YZ specs is, your cam timing is what will require the fatter jetting of the YZ, not just the pipe.


In my limited experience (one bike) changing the cam timing does not affect jetting very much, if at all.

WR jetting is a little weird, IMO, but after you get a load of the equally weird setup, as delivered (dime-sized exhaust outlet, throttle stop, airbox lid), it makes more sense.

My two rupies.

  • Hick

Posted May 21, 2002 - 09:03 PM

#10

Originally posted by BigDesto:
Hick- the stock needle on a 02 YZ426 is ejp correct?


Yes.

The EKQ I use is ½ clip leaner, and one size leaner on the straight portion (which governs mixture just off the pilot).





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