As far as air box mod you can can drill some half inch holes in the top of your air box lid so it will breath better. But get a few jets it will run leaner.
I bought it used off of a friend for $600. It has an aftermarket exhaust. The reason I'm looking to air box mod it is so I can jet the carb to both of the mods, instead of jetting it just to the exhaust. I'd rather get both out of the way now. It's still running stock jets and runs fine. Don't know which exhaust is on it right now, I'll identify when I get home.
I know, that's why I had to pick it up! First quad. Still need two new nuts for the rear wheels. Two were rounded and I had to use the nut removal tool I got at Sear's. He had all the tires facing backwards, which feels to weird when driving for me, so I rotated and now they're good. Much better traction for me.
How many holes should I drill? I'm thinking a 45 pilot jet and a 147.5 main? Seems that everyone likes those sizes.
I drilled 6 holes. On ebay they even have round plastic inserts with foam in side like little filters to help keep dirt out. I wish I would have just removed my lid during summer months because in the winter I think it's just too much air with how cold it is but depends on where you at. It was -2 here today.