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Jul 22, 2004 | 01:56 AM

kingofthemudholes

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400ex questions

yeah i bought a 2001 400ex today and i need to know what the stock size main jet is? and what jet i should be running with whitebrothers e series exhaust k&n filter with pre charger running no air box?

Jul 22, 2004 | 02:19 AM

kingofthemudholes

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400ex questions

and also i will be buyin keihan jets

Jul 22, 2004 | 03:02 AM

cals400ex

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400ex questions

stock is a 148. try around a 155-158. your elevation and temperature really matter so it is tough to guess.

Aug 5, 2004 | 12:07 AM

QuadZillas

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400ex questions

I have the same set-up and the stock main jet was a 148. I went to a 175 with the same set-up and it works great and after 25 hours the plug looks good.