I have a 2006 Honda 300ex for my wife and I jetted it but it pops on deceleration not to bad I looked at the spark plug and it looks light tan on the ceramic tip what should I do all I did to the atv is put a K and N filter and remove the air box lid

 

Thats means it lean in the idle circuit( popping on decell). Try going another 1/4 turn on the mixture screw (richer). You can go as much as 4 turns out from bottomed, and if you get that far, and it still pops on letoff, you need to go to a bigger pilot jet. Most guys go to the bigger pilot jet, due to better cold weather starting.
Welcome to the forums.

 

Ya, K&N with no airbox lid means more air flow. Must bump up gas flow to compensate. Start by turning you mixture screw a 1/4 turn at a time as hondabuster said. If it comes out (which i don't think it will) before it resolves the prob you will have to bump up the jet size.

Or alternatively you can put the airbox lid back on.

 

thanks guys this helps alot I will bump up the jet