Jetting Question???

8 replies to this topic
  • motoman393

Posted December 08, 2000 - 07:25 PM


I have a 2001' YZ426 with stock jetting. Today I had to buy a white bros high boy headpipe due to a recent crash with a KX80 which I crushed my stock header! I am wondering if i need to change the jetting and if so what to?? I have been reading this forum and have come to the conclusion that most people run a 168 main, 48 pilot, and 1 1/2 turns on the screw ...does this combo work? I live in Houston Texas at sea level if that helps! Also is the headpipe supposed to glow red it is freaking me out?? Thanks for all of your help I love this forum keep up the good work guys!


I get my kicks on a 2001' YZ426!
Friendswood, TX

  • DaveJ

Posted December 09, 2000 - 12:55 AM


I'm running a 165 and 45, at about 1.5 turns out. I tried a 48 and 50 to see if this would do anything for the off idle issue. Didn't. I think I also tried a 168, but came back since the bike seemed a bit snappier on the 165.

Oh, and I have the same setup as you, except I have a 2000, but don't ever recall my pipe getting red.

Try a richer mixture. And take a look at the plug.

I'll also assume you're not running race fuel.

And is your air filter clean?

  • motoman393

Posted December 09, 2000 - 06:05 AM


Thanks for the suggestions I will think i will richen it up a bit! No I am not running race fuel and my headpipe only glows red at night time while it is at idle (not when i ride it) i have heard this is normal on 4 strokes? And i clean my airfilter every ride or whenever it needs it! Thanks,


I get my kicks on a 2001' YZ426!
Friendswood, TX

  • BBRguy

Posted December 15, 2000 - 11:24 PM


hey Garret, looks like the jettng is right to me...although i forgot to mention that when we raced afte praticing the did backfir andhiccup a little on top end. by the way this is eric. just lettin ya know this is my new name, just registered it. aight see ya soon,BBWWWAAAAAAAAAAAPPP!

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  • mcarp

Posted December 25, 2000 - 07:13 PM


motoman-dude you're too lean as ALL YZ's/WR running stock jetting at sea level.Richen up- go to the 48, .75-1.0 turns on the fuel screw. Your problems will be a thing of the past and I betcha you'll notice a significant performance increase. You can temporarily help by turning out your fuel screw to around 2.5-2.75, but it's just harder to adjust when you change the pilot (you are going to change it,right?). Don't turn it much further than this, it could actually fall out-then you're really #^&#%#

Jetting is very bike/climate/rider specific, so you'll have to experiment. I guess my advise is to try the above and don't EVER hesitate to tweak your jetting one change at a time and feel for better performance. I just hate it when people make 1 little change, and proclaim perfect jetting. It's taken me 3 PJ's 4 MJ's, and 3 needles to tweak it for temps/pipe/altitude.

  • motoman393

Posted December 26, 2000 - 07:14 AM


Ok thanks for the advice I will goto the 48 pilot...what main jet do you think will work the best! I have worked on TONS of carbs and I am wondering how hard this pumper carb and this electronic 'stuff' is to work with! Feel free to post you jetting specs so I can see what your doing! Thanks mcarp!


I get my kicks on a 2001' YZ426!
Friendswood, TX

  • motoman393

Posted December 26, 2000 - 04:30 PM


ok im going to put in the 168 main and 48 pilot! I hope this solves my "problem"! But for a temporary fix (this weekend) I will turn my fuel screw out some!


I get my kicks on a 2001' YZ426!
Friendswood, TX

  • MrMXer

Posted January 01, 2001 - 07:01 AM


I am running a 165 main, 48 pilot and 2 turns on the screw at 1800' in Pa.. Works great for me. At sea level, the 168 may be the way to go. Just my 2 cents

  • James_Dean

Posted January 01, 2001 - 03:35 PM


I would be very cautious about turning the fuel screw out past 1 1/4 turns with a #48 pilot jet. This will risk plug fouling at low speeds.

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