09YZ450F Jetting question

3 replies to this topic
  • husky390or

Posted November 22, 2010 - 09:57 PM


I checked the jetting posts and none of them worked for me so here is what I have. Stock jetting, air temp is 25-50 degrees, altitude of 5,200', FMF Q4, Delkevic header, 06 CDI. The bike backfires when letting off from 3/4, 1/2, and 1/4 throttle. Do I need to raise the needle or change the pilot jet or both? It seems to smooth out a little in the 1/2 to idle range when I have the air screw turned out 2 1/2 to 3 turns but that's a little much for my liking. Thank you.

  • locomike

Posted November 23, 2010 - 07:06 AM


Go to a 48 Pilot and see if that solves it. After that, I would try raising the needle (dropping the clip) on position.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted November 23, 2010 - 08:08 AM


Start by checking over the exhaust to be sure there are no leaks in it at either end of the header. After that, baseline your pilot jet adjustment according to the manual, then evaluate the setting based on this:


Go richer if it fails the above test. By the info you give regarding your pilot screw setting, it looks like it wants a bigger jet.

The needle has little or nothing to do with the backfiring on decel, and frankly, if it's jetted perfectly, it WILL do that *a little bit*. A few pops on decel is normal, a constant loud popping is not. Some people at lower altitudes like to go with a needle with the next step smaller upper diameter to get better throttle response off idle, but this should not be necessary for yours at 5000' once the pilot is correct.

  • husky390or

Posted November 23, 2010 - 09:32 PM


Thanks guy's. According to that link and what you said gray, it seems to want a larger pilot jet. I threw one in tonight and will see how it runs on Friday.

Related Content


Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 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.