This just started happening I have never upgraded anything it is still stock but on decelartion it pop a threw the muffler why would this happen. Still have stock pop. and live on east cost so altitude isn't and issue Thanks

 

Theres an air cut valve, thats supposed to stop the leaning out of the idle mixture at decell (high vacumn). Check to see the hose is still attached and not cut or leaking.
Air lid stock, and properly installed?
If thats not it, are you using ethenol blended gas...or pure gas? Ethenol blended gas is a bit leaner than pure gas, and can cause the popping.
If youre using pure gas, and its still popping on decell, try a 1/4 turn richer on the mixture screw.

 

Popping is a lean pilot issue or an air leak. You can adjust your fuel screw to richen it up if you're all stock. You didn't take the airbox lid off and ride it without rejetting did you???

 

No did not take lid off totally stock I know I had to make adjustments to my 400 when I put the K&n kit and e-series pipe on but this just started making the popping. The only thing I have done is fool around with the idle it was set to lo when I got it and change the oil. Thanks

 

They come from the factory lean to meet EPA standards. You need to richen your fuel screw and better yet do yourself a favor and replace the stock one with an adjustable screw so you can just reach down at any time and make an adjustment. heres a link to some.
http://crfsonly.com/catalog/product_...oducts_id/1414

 

If you do want to make a change the HRC kit for an 06 is well worth the cost and it comes with everything you need and with recomended settings so their is no guess work involved....

Yes there are other ways to go faster, but most will be more money and/or more guess work

Good Luck