07' 450 popping bad on deceleration.....

8 replies to this topic
  • lftdjeep426

Posted February 09, 2009 - 05:45 AM


I just re jetted my carb after putting on a white brothers slip-on. I followed the Dynojet specs for a aftermarket exhaust under 3000 ft in elevation. I live/ ride at sea level in Florida. This thing really cracks and pops when I'm on the track and come into corners letting off of the gas. What could my problem be? Still not jetted right? Fuel Screw (which I don't even know what it adjusts)?

Hope you guys can shed some light for me. :)

  • Ga426owner

Posted February 09, 2009 - 06:27 AM


you need to know how the air/fuel screw works. Buy a adj fuel screw and search on adjusting fuel screws. For your area with temp and humidity changes it is critical to know this procedure.
What did you change in the jetting spec for the slip on?

  • lftdjeep426

Posted February 09, 2009 - 06:31 AM


That was a 160 main, Dynojet needle on position #4 and the fuel screw 1.5 turns out.....

  • grayracer513

Posted February 09, 2009 - 07:57 AM


If you did not change your pilot jet, the most likely reason for this is an air leak in the exhaust, most likely where the header joins the head, or where it fits to the mid pipe.

Main jets have nothing to do with this phenomena. It's either an air leak or a lean idle.


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  • lftdjeep426

Posted February 09, 2009 - 08:03 AM


I doubt it is an air leak. The slip-on is the non clamp style but the fit was so tight I had to use ice on the header and heat the slip on with a mild torch to get it to slide on. It is the tightest fitting exhaust I have ever dealt with. Why wouldn't the kit come with the pilot jet? I have checked the header fitment as well.

Recommendations:banghead: ?

  • StPeters21

Posted February 09, 2009 - 08:06 AM


the air leak would be at the head not the header/pipe joint. You still prob need to go up a couple in your pilot jet. I'm running a 48. I have no idea what my elevation is....but I'm in the midwest.

  • grayracer513

Posted February 09, 2009 - 08:34 AM


Why wouldn't the kit come with the pilot jet?

What kit?

Either way, if you read the link I posted, you should notice that some crackling on decel is actually a good sign. Nonetheless, if it's excessive (like nearly continuous every time you back off), come our on the pilot screw some. If you get to 2.5 turns and it's still not right, go up one size on the pilot.


  • YZThumper07

Posted February 09, 2009 - 09:03 AM


Agree..i had an 03 CRF450 with a crack in the head pipe right next to the head and the popping was terrible. Check all around your head pipe for any small cracks or openings..they can be hard to see sometimes. If thats not the case just try a 48 or even 50 pilot jet..Good Luck :)

  • lftdjeep426

Posted February 09, 2009 - 09:13 AM


You guys never cease to amaze..... TT is like old times of having your Dad there by your side while you work on your bike, only here Dad doesn't have to fix it when you can't figure it out!

I'll check it all out and hopefully fix the problem. I didn't know that a little popping was standard.

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