Installing your new aftermarket exhaust on your four-stroke motocross machine is simple and can be done by yourself in your garage in under an hour. We’ll walk you through the steps of installing an FMF system on a KTM 350 SX-F. Installing another aftermarket exhaust system on most modern four-strokes will be the virtually an identical process. Let’s get started!
1.2014 KTM four-strokes and up require you to remove the shock to remove the stock exhaust. You will not have to do this for any other bikes. To do this, remove the top and bottom shock bolts and linkage arm. To get the bolts out easily, lift the rear wheel up, and it will free up the tension.
2.Slide the shock down through the swingarm.
3.Working from the muffler to the header removing the mounting bolts. Most bikes, you will have to remove the side panel and seat to get to these mounting bolts. Don’t forget the two nuts that hold the header to the cylinder.
4.Remove muffler, mid pipe (if applicable).
5.Using your spring puller, remove the two springs that hold the header to the cylinder, and then remove the header.
6.Keeping your stock muffler handy, you’re going to want to use the stock rubber grommets for the mounts on your new aftermarket muffler. Use a flat head screwdriver to force the stock grommets out of the stock muffler. Use a bit of WD-40 to make installing the stock grommets onto the aftermarket muffler easier.
7.Install the new header. Tighten the cylinder mounting nuts finger tight for now.
8.Apply high temp silicone to the inside of the mid pipe or outside of the header to make for a better seal.
9.Slide the mid pipe on to the header. This may take a bit of twisting, but it should slide on without much effort. Do not install the mid pipe mounting bolt just yet.
10.Now that the mid pipe is on, you can reinstall the shock and linkage (if you have a newer KTM). Be sure to torque to spec and use a bit or red Loc-Tite for some insurance.
11.Now is a good time to install the new header springs using your spring puller.
12.Use a bit of high-temp silicone again on the inside of the muffler, and slide the new muffler on the mid pipe. Again, you may have to wiggle it on a bit.
13.Install the mounting bolts for the muffler.
14.Make sure everything is aligned and begin to tighten all the mounting bolts starting from the muffler, moving towards the header.
Now that your new exhaust system is installed, you’re going to want to wipe down the system with alcohol to remove finger prints and oils from the exhaust. This will give your exhaust the best possible look when first starting your bike. It’s always best to do a quick heat cycle before you go ride. Don’t be alarmed if the exhaust glows bright red the first few times you start your bike, this is normal and the metal should turn to a factory bluish tint around the welds once cooled.
With all exhausts, having fresh packing helps keep the sound down, but also maintains the power. Check out our full how to repack your muffler video and instruction sheet if you think your exhaust is due for some fresh packing. Most aftermarket exhausts come with a spark arrestor insert, so don’t to forget to install the insert if you are riding where a Forest Service approved spark arrestor is required. Installing these is easy and just requires removing the end cap with an Allen wrench.