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Re-jetting?

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I bought a new fmf full exhaust front to back (4.1 with a mega bomb header) for my kx250f I hear lots of people saying you have to re-jet and others saying you don't, unless its running lean. So what's the deal do you have to re-jet or only if it runs lean, if so how do I tell if its running lean?

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Rejett. I believe you will have to rejett a little bit more rich. Popping is a sign of bad jetting for 4 strokes. (May have to wait for a 4 stroke guy to chime in tho) Acceleration and deceleration popping.

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I bought a new fmf full exhaust front to back (4.1 with a mega bomb header) for my kx250f I hear lots of people saying you have to re-jet and others saying you don't, unless its running lean. So what's the deal do you have to re-jet or only if it runs lean, if so how do I tell if its running lean?

 

I live at 7000' so I'm spoiled, factory jetting with the thinner air usually isn't too far off for me. If you're having issues, just doesn't feel right, JD jet kits provide the product, and more important, the instructions to put you in the ballpark pretty quick for most situations.

 

Mike

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Some signs of running lean -

 

Popping on deceleration

Overheating 

Loss of power

Spark plug electrode white in colour

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from the FMF site

Jetting Results

  • Main Jet
  • 180
  • Pilot Jet
  • 42
  • Needle
  • NCYS
  • Needle Position
  • 4TH
  • Power Jet
  •  
  • Air Screw
  •  
  • Fuel Screw
  • 2 1/2

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