Just as with any motorcycle, the muffler packing on a KTM needs to be replaced from time to time. The packing, which is similar to fibreglass insulation, dampens noise. It fills with carbon, compresses and loses its ability to deaden sound with use. Replacing the packing can be done in less than an hour if you have the right tools and know a few good tricks.
Remove the exhaust canister from the motorcycle and find a clear and clean workspace. Examine the canister tip. Like most motorcycle exhaust systems, KTM often uses rivets to fasten the cap onto the exhaust canister. If they're small bolts, they're very easy to remove, but they're more likely rivets and need to be drilled out. Fortunately, the centre of the rivet centres your drill bit and the material isn't especially hard. Take your time and don't let the drill bit "walk out" of the hole as you drill through the rivet. If the stem doesn't push all the way through, you can pop it out after you've removed the exhaust tip; use a small punch and a mallet.
Using Masking Tape
Once you've removed the exhaust "core" or "baffle" and discarded the old packing, lay your new packing out in a sheet. You'll roll the exhaust core in the sheet like rolling a cigar. Roll the material on snug, but not as tight as you can get it. Once you've wrapped the core, wrap masking tape around the core to hold the new packing in place. Wrap at both ends and in the middle. The heat of the exhaust will burn the tape away, which is fine. Meantime, it will allow you to pack the muffler thoroughly and evenly.
Pack Tightly and Trim
Don't be stingy with the packing. Remember, you're replacing the old packing because it's compressed and full of carbon. So, you're going to make a larger bundle than the bundle you removed. You want it to be larger and hang out the ends so it will pack in place firmly. When you replace the exhaust core, trim excess stuffing before replacing exhaust cap, rather than trying to get the perfect amount when you're wrapping.
Other Tools and Supplies
You may want to use a mechanic's mallet to gently tap off the exhaust cap. Carbon can get between the exhaust cap and exhaust canister and make it a bit difficult, otherwise. If the exhaust cap fit is loose, you can use high-temperature silicon sealer to snug the seal. The best supplies you can have for this task are a pair of thin rubber gloves and plenty of rags and contact cleaner. Expect a lot of sooty carbon.