2005 YZ450F Jetting Spec

17 replies to this topic
  • James_Dean

Posted October 16, 2004 - 09:09 AM


What is the 2005 YZ450 jetting?
pilot (45)
3 turns out (?)
needle code (NFLR)
clip position (#4)
main jet (165)

I'm jetting a '04 YZ540F with WB exhaust and would like to compare.

  • undrdog

Posted October 16, 2004 - 11:32 AM


Pilot jet #45
Jet needle-Clip position..NFLR-4
Main jet #165
Is this enough info ???? :cry:

  • James_Dean

Posted October 16, 2004 - 08:25 PM


Thanks undrdog...

Is the standard fuel screw setting 1 1/2 turns?

  • YZ250F_Rider

Posted October 16, 2004 - 10:00 PM


yes, but it's lean throughtout with the stock jetting.

  • ovrrdrive

Posted October 17, 2004 - 02:46 AM


yes, but it's lean throughtout with the stock jetting.

Yeah, and it's slow as all get out. I can run faster than this crappy thing...


How was that?


  • YZ250F_Rider

Posted October 17, 2004 - 05:40 AM



I dont think I can run faster than it, but I have found it's niche in life. I use it to train with now. The added 12 pounds of weight and the fact that it's harder to corner causes me to be more aggressive riding it. That lets me beef up and treat the 250 like a little biatch bike. :cry:

  • Thumper38

Posted October 19, 2004 - 07:38 AM


I have found this to be true too, I went to 168 main and I need to go up on the pilot too. What jetting are you running? I still have it poping when I chop the throttle (on deceleration) so it is lean to me. Please correct me if I am wrong! :cry:

  • YZ250F_Rider

Posted October 19, 2004 - 08:01 AM


They put a 170 main in with the bike's manual, so I just put that in and it runs fine. I havent played with the needle yet so it's still a bit lean too. It feels like it could go a notch richer as well.

I turned the pilot screw out 1/4 - 3/8 turn to stop the backfiring on decel. Just do it a 1/8 turn out until it just stops.

  • Thumper38

Posted October 19, 2004 - 08:08 AM


I came out 3 turns and it is still backfireing, so I guess I need a bigger piolet? :cry:

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  • YZ250F_Rider

Posted October 19, 2004 - 08:27 AM


what main are you running?

  • Thumper38

Posted October 19, 2004 - 09:03 AM


A 168 main!

  • YZ250F_Rider

Posted October 19, 2004 - 09:24 AM


It's kinda cold up there isnt it? I would be tempted to up the main, and then redo the pilot setting. and dont forget to check the needle.

  • ovrrdrive

Posted October 19, 2004 - 01:59 PM


I'd go up as well. I put a 168 main in mine too. For the most part it feels really good but I did feel it starve once on WOT. As its starting to cool off I'm gonna drop the 170 in soon.

My PJ felt a little lean with the 45 in it until I put the PMB SA exhaust tip with the quiet insert on the pipe. That was just enough restriction to put the pilot circuit spot on.

Until it cools off that is.

  • motojoe44

Posted October 28, 2004 - 05:27 PM


I purchased a new YZ450 and it ran lean as well. I put a WB Carbon Pro pipe and Twin Air Power Filter kit on it and it got even leaner. The local shop told me to put a 48 slow jet and 170 main in it to fix the problem. It ran better with this setup, but it's still lean. I went one richer on the needle and came out another half turn on the fuel screw and it's still lean! Not sure what the problem is with this bike but I can't imagine that I'm still lean on the jetting after going up on then entire circuit.

I talked to White Brothers and they said to go back to stock on the needle and turn the fuel screw out to 3 1/2 turns with the 48 slow and 170 main. So, I'm going to try that this weekend and see how it runs.

If anyone has had any luck jetting the 05 YZ450 please reply so I can spend more time ridding and less time jetting.


  • Thumper38

Posted October 29, 2004 - 03:59 AM


I am goning to the same set up tonight with the stock setup, I checked (twice) for any air leaks and found nothing. I just think they are very lean from the factory! I will try the 170 main and a 48 pilot with the needle stock. :cry:

  • YZ250F_Rider

Posted October 29, 2004 - 04:04 AM


sure you can still be lean. You have uncorked it considerably from stock. Dont forget cold air will make it run leaner as well.

going too rich is real easy to tell, and wont damage the bike.

  • tricksta400

Posted October 29, 2004 - 04:53 AM



  • YZ250F_Rider

Posted October 29, 2004 - 06:52 AM


it will pop and backfire under acceleration and the plug ceramic wont ever color to a tan color.

your best bet is to always start rich and work done to the bet jet size. but starting from stock and working up to a richer jet is safe enough.

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