'08 Deceleration popping

5 replies to this topic
  • ewilly

Posted September 09, 2008 - 06:37 PM


I just picked up a used '08 YZ450F with 7 hrs on it. The seller says the jetting is stock and I am in Phoenix around 1300 feet at 95 degrees. When I test rode it and after warming it up it would produce a popping sound when decelerating which in some conditions I would consider a lean codition. The seller stated that he was told that it was a normal sound and it wasn't like some lean detonations but not as loud and more frequent.

Does anybody have input on this? Is it normal or do I need to make some changes?

The power feels good but it is not idling real consistent.

Thanks for your help!


  • grayracer513

Posted September 09, 2008 - 06:42 PM


Some decel popping is normal, and a sign of correct jetting if it does it about half the time or less. Constant loud exhaust backfire is abnormal.

It almost always results from an air leak in the exhaust, lean pilot (idle circuit) jetting, or a hot start plunger not fully seating.

  • sean3239

Posted September 09, 2008 - 07:20 PM


I just bought an 08 YZ450 and live in Phoenix as well. It had some decel popping (although nothing as bad as my 06 when I bought it). For the 08, I went up to a 48 (from 45) on the pilot which took the decel pop away and bike runs great. Because it was summer, I was right on the edge of really not needing the 48, but as the weather cools, I think its the right thing to do. I think you will find the same especially if you think you have bad popping on decel.:thumbsup:

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  • ewilly

Posted September 09, 2008 - 09:41 PM


First of all, thanks for the reply! Gray I think your description is right on because there is no loud backfires. I will check tightness on all exhaust and then probably go up on the pilot jet like Sean suggested. Is it necessary to make any other tweaks and how much are these motors affected if I wanted to go up and ride at 8000 ft elevation. :thumbsup:

How about swapping silencers does the jetting change significantly? Thanks in advance!


  • ewilly

Posted September 09, 2008 - 10:55 PM


Sorry it didn't look in the general section first. I don't see anything in there about the shorty muffler mods? Hint Hint

  • grayracer513

Posted September 10, 2008 - 06:13 AM


General section? You mean the Common Threads sticky?

There's been no one come back and say categorically that they've done anything to the '08-9 muffler to successfully correct it yet.


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