Jetting Recommendations Please - 02 YZ426

2 replies to this topic
  • xnofriendsx

Posted November 23, 2007 - 11:42 AM


Can someone please recommend some jetting specs?
The settings below were decent when i was living at sea level, but i recently moved to 3500ft elevation and just did the BK Mod with .5 sec squirt. It was at around 3 sec squirt. I will be testing it in a few days. I am yet to start it up yet after i did the BK Mod the other day.
Two Questions:
1. What settings below should i change due to the BK Mod?
2. What settings below should i change due to the elevation change?

Thanks for any help.

Model: 2002 YZ426
Timing: YZ
Main Jet: 162 (stock)
Pilot Jet: 42 (stock)
Starter Jet: 72? (stock)
Leak: ?
Fuel Screw: Zip Ty: 1.5 turns out
Air Box: No Lid
Pipe/Muffler: Stock
Altitude: was at sea level, then just moved up to 3500-5500ft
Temp: 30-70F
Humidity: <20%

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  • grayracer513

Posted November 23, 2007 - 02:56 PM


Theoretically, a 4200 ft increase in altitude would require you to lean your jetting by a factor of about .96, which would mean a 155 main and a 40 pilot. (Don't fiddle with the starter jet until there's some proof you need to. Your carb has no leak jet)

However, what I suggest you do is try the bike as is first. YZ426's had a rep for being lean on delivery, and you may find it runs really well just as it is, or perhaps doesn't need as much correction as the charts would indicate.

  • dc671

Posted November 23, 2007 - 03:03 PM


xnofriendsx sorry to hi jack your thread...

grayracer I'm hoping you can help me out with my jetting issues also? I have an '06 YZ450F and I am located in the San Francisco Bay Area. I replaced the jets with the FMF kit. Main jet is 150 and Pilot Jet 48, went 2 turns out on the fuel mixture screw and the have the needle clip at the # 4 groove from the top. The problem I am experiencing is it still backfires when I let off the throttle and sometimes doesn't idle that good. Any suggestions? Thanks for the help!


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