yep, this is exactly what i did with the stock mufflers on both of my bikes.
Taking the "screen" (or cat. converter so called thing) out will not make the exhaust louder. you have to modify the baffle plate to make it louder. removing the screen will do exactly what 2 stroker said.
That screen will clog up with oil and rob power from your engine once you hit about 500 miles.
removing that screen frees up the exhaust flow and you will actually get a performance gain from it. Not just in what you feel, but in actual mph (altho it may only be a TINY increase, you take what you can get with these things) and it's a free mod that's simple to do.
on one of my bikes, (49 c.c. 2 stroke) i have the stock muffler welded to the end of an expansion chamber. I did remove the "screen" and modify the baffle plate inside the muffler by drilling a couple of small holes it it to improve flow. when i say baffle plate, I'm talking about the round disk on the end of the baffle tube that slides up inside the muffler, not the muffler end cap.
But really, this set up isn't much louder than a weedeater.
On my other bike (66 c.c. 2 stroke) i did the same thing...removed the "screen" and drilled holes in the baffle plate in the muffler.
This muffler is hooked to a long straight pipe, and it really sounds good.
Not too loud, but it has a nice deep throaty sound.
get that screen thing or cat. converter thing (whatever they are calling it) out of the muffler, it just gets clogged, robs power and will not increase the exhaust noise.
i live in a really rural area where people ride golf carts and 4 wheelers on the roads, so no one pays attention to the little bit of noise that comes from my bikes.