2001 yz 426f

12 replies to this topic
  • B_Powell07

Posted April 21, 2014 - 11:31 AM


I need some help or ideas.
On deceleration my 01 yz 426f popping like crazy not sure whats up any ideas would be great

  • grayracer513

Posted April 21, 2014 - 12:19 PM



  • B_Powell07

Posted April 21, 2014 - 06:51 PM


Its not letting me click on the link grayraser513

  • B_Powell07

Posted April 21, 2014 - 06:54 PM


Another thing I noticed when the choke is out it runs fine no popping at all but as soon as I push the choke in it starts popping during deceleration

  • seacraft69

Posted April 22, 2014 - 07:13 AM


That link will probably be telling you your lean.

  • grayracer513

Posted April 22, 2014 - 08:09 AM


Not exactly.


Anyone else having a problem with  that link?  I'm not.


Here's what the post says:



Excessive decel popping is almost always the result of one or both of two things; lean idle mixture or an air leak in the exhaust. In some engines it can be brought on by a very excessively rich condition, but this is much less common. You should usually troubleshoot it by looking for the exhaust air leak first, because otherwise, you will end up with a bike that's too rich to run right because you fattened it up to cover over a pop that was actually caused by something else. Aftermarket pipes have a slip fit midpipe/header. Check it.

Lean idle jetting can be as simple as a fuel screw adjustment, or it can be an undersized or clogged pilot jet. Another, less common cause is a hot start plunger stuck partly open.

Besides, a little bit of popping on decel is normal for a YZ450, and IMO, any YZ450 that never pops at all is too rich on the pilot.

The '06 is, as was pointed out, built lean. I run a 45 pj/165 main, and it's worked well so far. When the bike first came out, in the cold months, a lot of guys immediately went with a 48/170 set up, and many of them dropped down to the 45/165 as the weather warmed up.

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  • seacraft69

Posted April 22, 2014 - 08:45 AM


About the links, in the common threads section only some of them work for me. But I use my phone for innerwebs so I put it down to that. Also good to know about the 06 since thats what I have.

  • grayracer513

Posted April 22, 2014 - 09:03 AM


Don't have to use your phone...

Attached Thumbnails

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  • B_Powell07

Posted April 22, 2014 - 10:05 AM


Thanks grayraser513. . I have zero air leak on the exhaust I checked the boot on the carburetor side and air box and its fine no dry rot. I'm starting to lean towards the jetting now because when the choke is on 0 popping when you ride but as soon as the chokes of it dies

  • grayracer513

Posted April 22, 2014 - 10:18 AM


Then the problem is the pilot jet either clogged, too small (not likely since it used to be OK), adjusted wrong, or the screw or O-ring is missing or damaged.

  • 72degrees

Posted April 22, 2014 - 12:35 PM


Our very poppy 04 450 is much less poppy (thought not completely) now with an o-ring that had gone missing replaced with along with a new after-market knurled adjuster. Easier to start too.

  • grayracer513

Posted April 22, 2014 - 01:30 PM


Our very poppy 04 450 is much less poppy (thought not completely) 



It's not supposed to be completely free of it.  They'll crackle on decel if everything is set as it should be. 

  • 72degrees

Posted April 22, 2014 - 01:39 PM


It still does a little when running back down the hill on a closed throttle or under hard braking for a hairpin, but not as much as it did. I might have gone a tad too rich by adjusting by ear on idle speed though. At least it's easily tweaked now and it is certainly going well.



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