Need help with jetting.

5 replies to this topic
  • Motone82

Posted October 16, 2004 - 06:55 PM


I have a 2000 YZ 426 with a Pro Circuit T-4. I just put the pipe on and it runs like crap. Popping very bad. I called Pro Circuit and they said they didnt have any books on the jetting for my bike. Cna anyone please steer me in the right direction? Thanks

  • Fastest1

Posted October 16, 2004 - 07:20 PM


I am assuming it was running great with the stock pipe? Does it pop under acceleration or deceleration or both? Does pulling the choke help? Usually if the pipe actually increases power, you will need more fuel. Tell us where in the power it is acting up (low, med or high throttle)? Does it start well? Have you changed fuels? Is it alot colder where you are all of a sudden?

  • WR426madness

Posted October 16, 2004 - 07:27 PM


Dude try a 160 main, stk pilot jet, fuel screw 2 turns out, needle 3 nothch from the top. :cry:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Motone82

Posted October 16, 2004 - 08:22 PM


Ok here goes. I had a DSp pipe on it. 172 main and I believe 46 pilot. Ran great. Switched to the T-4 and it starts ok but doesnt idle well and pops like mad decelerating. Wants to die when I come to a stop. Thank you guys for your help.

  • YZ250F_Rider

Posted October 16, 2004 - 10:04 PM


turn the fuel screw out a 1/4 turn and see if it helps. Also check that the float works correctly.

  • ovrrdrive

Posted October 17, 2004 - 02:49 AM


Read this article to understand a little more about jetting then try setting your fuel screw the way they describe in the article.


If mine were that lean, I'd see what jets were in it and go up one level on the pilot and main and see how it runs from there.

Related Content


James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

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.