need some help jetting/ airbox lid

First off before my jetting ques i want to know what type of air box mods some of the woods riders have on here. like i want some better flow but i go through a lot of creeks and mud all the time so i need to keep it covered as much as possible

Now.....

I have rejetted my 400s couple of times and mine seems to be almost perfect but if you start it and try to punch it fast when reving some times itbogs out and the dies and you here a quick back fire. but when im riding it doesnt seem to have any problems. Now gfs 400 is doing same thing but a tad worse. Im thinking its too rich but could somebody confirm that so i know which way i should start jetting it again.
Thanks