Jetting Question

2 replies to this topic
  • icon27

Posted April 02, 2009 - 04:06 AM


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

Timing: YZ
Main Jet: 160
Pilot Jet: 38 [COLOR=Red](edited from 40)[/COLOR]
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

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • wondermuscle

Posted April 02, 2009 - 01:22 PM


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....

  • grayracer513

Posted April 02, 2009 - 01:35 PM


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.

Related Content



Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.