wr250x popping on decel after mods bad?

A small leak in the exhaust can produce a little popping on decal.

Its set to 3 3 .5 8 4 4 Cant imagine I have an exhaust leak but I can look around I guess

So reading all this stuff on the internet freaks me out as much as looking up symptoms on WEB MD. So this Friday I made a Dyno appt. with a highly rated and recommended person/business to check my lean v.s. rich ratio. Turns out I was still a bit on the lean side with the FMF programmer. Short story long, he dialed in my programmer, took off the air box door, and took out the spark arrestor and it now freaking RIPS! Seriously crazy different. It is pretty loud though, so I might put the arrestor in again. After 100 miles only a few pops on deceleration. Love this bike...just stresses me out way more than my last Roadstar on screwing up the engine.

Most everyone who does the typical mods (exup, AIS, and air box lid removal; full exhaust; and programmer), don't tend to do the C.O. mod (there are posts on here about how to get into C.O. mode). If you are having some issues with fine tuning the fuel mixture, set your programmer to your preference, and if you are having issues adjust the C.O. +/- for fuel. This should help with running too lean and any popping. I enjoy C.O. mode just for keeping miles off the bike and most of all, keeping an eye on RPMs. (note: gearingcommander is an excellent website and tool.) Hope this helps.

I might be a noob, but what the hell is CO mode? What does it stand for? I've read posts about it, but nobody says WHAT it is...

It is literally on the display when you enter into it. CO then it will say C1 (cylinder 1) 0 above (n1) whatever number yours is or change it to. It is a way for the fuel/air to be changed. It most likely stands for computer or cylinder/oxygen or carbon monoxide. If you enjoy tinkering or just want to try it, it doesn't take long to setup and doesn't hurt the bike. You can leave it for later use or disable the mod.

There are plenty of posts (some with pics) on how to do it. Here's one.
http://advrider.com/forums/showthread.php?t=538181&page=3