yz450f carb fitment with airbox mod

6 replies to this topic
  • rmx250rider

Posted November 29, 2009 - 05:42 PM


what year carbs off a 450 will work on a 98 yz400f? and what will happen if I cut out the devider on the boot right before the carb?

  • rmx250rider

Posted November 30, 2009 - 06:52 PM



  • grayracer513

Posted December 01, 2009 - 06:43 AM


Describe the divider.

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  • rmx250rider

Posted December 01, 2009 - 12:02 PM


its right before the carb... The air cleaner joint. it has the divider, for the smaller jet on the bottom of the carb and it has the main opening for slide... its kinda like the powerwing, but it comes stock in the joint.

  • grayracer513

Posted December 01, 2009 - 12:44 PM


Don't modify that. I wasn't sure that the earlier air boot was also made that way. It is the result of a lot of expensive flow bench work, and is designed to make the whole thing work better.

Provided that the mounting diameter is the same, and I think it is, any of the FCR-MX39 carbs should work with a minimum of rejetting.

  • rmx250rider

Posted December 01, 2009 - 03:48 PM


What benifits would help from going to a 450 carb?

  • grayracer513

Posted December 01, 2009 - 04:08 PM


Refinements, mostly, like many things. The newer ('05 and up) carbs have a more sophisticated accelerator pump system that features a leak jet, and all FCR-MX models, as opposed to your FCR, are a little more refined insofar as mid throttle metering, etc. Nothing Earth shaking, but if your carb is worn out or damaged, it's probably going to be easier to find a newer carb still in good condition, and they will work a bit better in the long run. I wouldn't recommend it as a hop up of any kind.

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