A new exhaust can make an enormous difference for a Honda 400EX. The power and good sound gained from this fix can’t be matched by any other replacement or add-on. However, this process, though quite short, can be relatively costly.
1. Choose an exhaust kit that will provide the best powerband and sound for the way that you use the ATV. Exhaust kits can be found at any major motorcycle and ATV supply store (see Resources below).
2. Unscrew the frame bracket bolts and remove the hose clamp that holds the exhaust lead on. Pull the entire exhaust assembly away from the atv frame and out of the exhaust port.
3. Rub a small amount of heavy heat silicon around the end of your new exhaust leads. Slide the leads into the exhaust port and bolt the lead to its frame bracket. Reattach and tighten the hose clamp that was previously located on the exhaust port.
4. Again rub a light amount of silicon on the inner tip of your new exhaust end. Slide this on to the exhaust leads, and clamp and bolt it in. Make sure that the entire exhaust assembly is completely secure.
5. Have your ATV re-jetted for the new exhaust setup. Refer to the exhaust kit manual for specifics.