Read on a Swedish site thet you could gain about 5 hp by ripping out the stuffing in your pipe (not the silencer). Comments? IT would surely be noisier but, no pain no gain! There was a comment about rejetting afterwards was necessary...
I own a 1994 KDX 200. I have done the modification found at http://justkdx.dirtrider.net/ Tech tips Building Your Own Secret Weapon,
1989 - 94 KDX200 Pipe Modifications. Not all that hard to complete, but takes a steady hand and delicate welding to get things back together. You have to use a chisel and hammer to seperate the metal screen from the pipe. Yes it does produce alot more horse power from the bottom to top end. When you get all done, pait with high temp gloss paint. Doesn't produce as much top end/revs, but saves about $200 for a FMF pipe.
YES I GUTTED MY PIPE, AS DESCRIBED ON THE MAIN PAGE..I CHUCKED THE HACK SAW,USED A SAWS ALL. IT IS A VERY MESSY JOB AND YOU WILL DISTORT THE EDGES OF YOUR CUT PRYING OUT THE SCREEN. ALSO REMEMBER THERE IS NOTHING STRAIGHT ABOUT A PIPE, IT IS VERY AWKWARD, HAVING 2 PEOPLE FOR CUTTING AND TACKING WOULD BE EASIER. AS FAR AS PERFORMANCE CAN'T HELP YA, I'M STILL WAITING ON A REAR WHEEL, BUT IT SOUNDS LIKE A BIKE NOW.
I've done this surgery to my pipe (87 kdx 200)and man does it ever boost the bottom-mid range power and it does feel like you gain about 5hp! As mentioned it is alot better to have another person to help with the procedure but the end result you will like alot.I don't know what year yours is ,but mine you have to take a hammer and chizel to remove the screen inside the expansion chamber(the hardest part of it)But the most important part is to make sure you make marks on the pipe before you cut it apart so when it comes time to weld it back together it will line bake up the way it was before or it will not bolt up in stock form causing you alot of grief!Good luck with the mods. if you try this.I know if you do the end results will make you smile when you roll the throttle!(P.S. I didn't have to rejet mine)