Jetting specs

4 replies to this topic
  • critter

Posted May 05, 2003 - 04:09 AM


Ok...02 Canadian WR426, no lid, Big Gun Race, YZ timed, bk'd @.05...168 main,45 pilot, OBELN #3, fuel screw @ 1-1/2. Seems to be rich, popping and snorting thru 1/2 throttle. Would ACV mod cure this or drop down on the pilot or the needle or main jet. I'm a long time 2-stroker and this 4 stroke jetting is killing me. /bike/ubbthreads/images/graemlins/smashpc.gif

Any help would be appreciated
Im at 500 -700ft sea level

  • Chris_from_Oz

Posted May 05, 2003 - 04:44 AM


Critter, my Aussie WR (same spec' as Canada) runs 162 main, 42 pilot, stock needle dropped 1 notch, fuel screw at about 2 turns out, give or take an eighth of a turn, depending on temp'. I am at sea level, but bike runs great in the mountains on the occasions I head up there. My bike is set up similar to yours with BK/GB mod', no lid, YZ timing etc, only difference is I run a YZ muffler. I agree you are probably a little rich, mine used to splutter and fart through the mid-range too. I have heard of good results from the YZ needle, so I will try that next, but i'm happy with it for now, I just like tinkering. Good luck with it. :)

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  • uechi45

Posted May 05, 2003 - 07:26 AM


My sons 01 WR426 was doing the same thing. The exhaust is stock but uncorked. We removed the air box cover and put in 175 main jet, raised the needle one position, and turned out fuel screw 2.5 turns. Bike ran O.K. but when we put the Yamaha GYTR quiet insert in the mid was all screwed up. I just fixed it. Put the 165 main jet back in, left the needle one position higher, turned in fuel screw to 1.75 turns, replaced the airbox cover but without the baffle. The bike runs superbly. You can snap the throtle from idle (in gear) or roll on smoothly and there isn't any more crap going on in the middle. When adding in the quiet insert you loose a little bottom and the bike runs hotter but that we can live with. Good luck.

  • RPS

Posted May 05, 2003 - 07:41 PM


I called Yamaha Tech and asked for the jet specs for running the stock exhaust with the GYTR baffle.

1. Up two sizes on the pilot jet from stock.
2. Put in smaller #40 leak jet. The stock leak jet I beleive is a #90 for both the 03' WR450 and WR250.
3. Fuel screww two turns out.


  • Descendents

Posted May 06, 2003 - 04:31 PM


I just put a OBELN needle in this past weekend on clip #3 and kept everything else stock in the carb. It runs great, seems to rev quicker and rips through the gears. No sputters, pops or misses. I run close to your elevation, so I would say you are probably rich. My plug is black still so I am going to try coming down on my main jet. I was told that if you put a E tapper needle in, to go down 5 on your main jet. The difference from going to the OBELN needle is great, you can really feel it.


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