yz426 jetting

what altitude are stock bikes jetted for?

As lean as most of them have been lately, I'd guess 2500-3000 feet, but I don't know what the actual target altitude is supposed to have been. I run the 165 main jet that my '06's were delivered with at altitudes running from sea level to 3500 feet with no real problem, but I did bump the pilots up a notch.

The 426 comes jetted for Sea Level at 70 degrees. Be sure to use Motoman's jetting chart as shown in the posts above, it will get you real close to where you need to be.

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