Which runs leaner, 426 or 400

3 replies to this topic
  • Dougie

Posted April 09, 2002 - 04:04 AM


Do the 426s require a leaner jetting on average than the 400's? Or is it vice versa? I assume I should not be looking at jetting ranges for the 426s for my '99 400 but it seems the 426's in CO are jetted leaner than my 400. Just wondering if this is correct as I battle my jetting demons.

  • SFO

Posted April 09, 2002 - 05:15 AM


I run leaner jetting in my 97mm big bore than I did in my stock motor.
I believe this has something to do with there being a larger vacuum signal, but am unable to grok it fully enough to explain.

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  • skthom2320

Posted April 09, 2002 - 07:36 AM


They are different due to CDI maps, etc.

I didn't notice that you were in Colorado when I replied to your other thread.

You may very well just be too darn rich all across the board.

I think I explained pretty well how to richen/lean your entire range. Go to it and let us know your results!

  • jbird

Posted April 09, 2002 - 07:51 AM


I don't think it's a matter of being jetted leaner or richer it's more a matter of running to proper jets for your displacement. The larger the displacement the smaller the jets you can run to achieve proper jetting. If you were to compare a 125cc 2 stroke you will find the main jet is much bigger than the main in a 250cc. It seems backwards but that's the way it is.
A 426 then would run smaller mains than a 400. That doesn't mean the 426 is really any leaner. It just uses smaller jets. You can't compare your 400's jetting directly to a 426.



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