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Jetting Question

3 posts in this topic

The cold weather is here and I've fattened up my jetting for the cold air.

Timing: YZ

Main Jet: 160

Pilot Jet: 38 (edited from 40)

Starter Jet: 70

Leak: N/A

Fuel screw: 1 1/4 to 2 1/2 turns out

Needle: stock at #3 position

Air box: unmodified w/Twin Air filter

Pipe/muffler: Powerbomb SX/Powercore 4

Altitude: 5700 to 6200 feet

Temp: 55-65 F

Humidity: 15% to 35%

I'm happier now with theses changes versus the mid summer specs with the cold weather. Just an occasional pop when chopping the throttle, generally happening when the track is just watered. The bike feels faster in the cold weather. I can't wait to ride a 450 at sea level.

Runs better with the 38 pilot jet at 65 degrees.

Summer specs:

I also live in Colorado and just bought a YZ450F. I am going to use your settings as a starting point to get the carb ready for this altitude. One thing I dont find in the manual is what your calling the starter jet which is set to a 70. Can you tell me where that is or if it goes by a different name in the manual? Also, When setting the needle clip to 3 (manual says stock is 4) that would be 3 notches from the top of the needle correct? Any help is appreciated with set up. Im a old 2 stroke guy so the 4 stroke thing is new to me.... Thanks

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The starter jet is next to the main and the pilot. You acces it the same way you would the pilot or main.

Yes, you count needle positions from the top. So 4th pos would be the fourth down from the top.

Beinig a 2stk guy, you should be a jetting master....

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One thing I dont find in the manual is what your calling the starter jet which is set to a 70.
See page 4-12 and 4-16 of the manual.

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