Jetting Question

5 replies to this topic
  • c-man

Posted July 11, 2007 - 08:47 PM


Recently baught an brand new 06' 450F and want just a few ideas on jetting it. I have looked at the thread at the top of the forum and cannot quite figure out how to use the formulas seen there. Bike is all stock and I know they come jetted pretty lean. In the spring when I baught it is would pop and crack a lot on decelleration, so I put one size bigger main, one size bigger pilot, and backed the pilot screw out 1/2 turn. Now that it is a little warmer outside it seems to start a little hard, occasionally backfire when starting warm, and surges just off of idle when riding down the road. I understand that they do not run like a traditional 4-stroke down the road due to lighter flywheel weight, etc, but my 01' 426 seemed to run a lot smoother than this does at this point. I am at about 3500 to 4000 feet in dry climate and want it jetted for about 80 degrees F. Seems to me like it may now be a little rich?? Advice welcome.



  • WB450

Posted July 12, 2007 - 07:08 AM


Look up top where it says "ALL YZ450 jetting specs". Not to be a dick, it's helpfull.

  • ben_suhard

Posted July 12, 2007 - 07:47 AM


MXA mag says to change the needle to an NFLR and pilot to a #45. Do you know how to adjust the fuel screw? http://www.motocross...032722A4D5D52E3

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  • treygreen

Posted July 12, 2007 - 07:53 AM


With my 06 all I did was change the pilot to a 45 and she is a one kick wonder. I did also buy a gytr fuel screw and set it to about 2 1/2 turns out. You might want to go back to the stock main jet.

  • grayracer513

Posted July 12, 2007 - 08:19 AM


You may be a bit rich. One thing though, is that way too much is made of decel backfiring. If a YZ450 never does that at all, it is too rich at idle. Some is normal.

I run ours with a 45/165, stock needle in #4. The NFLR needle may be an improvement, but probably not much, as it's the very same taper profile cut so that #4 on the NFLR is one half step leaner than #4 on the stock one. So far, ours has run pretty well in conditions much like yours with just an occasional tweak of the fuel screw.

  • Ga450owner

Posted July 12, 2007 - 08:57 AM


For my Altitude 900-2000ft here in Ga the NFLR needle was the well as 45 pj 168mj

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