RS-9 Sound Insert Kit: How to Tune Your Muffler Volume
By Yoshimura R&D of America, Inc. | Published: 2026-10-31
Category: How-to Guides
The INS-RS9D-K insert quiets RS-9 and RS-9T mufflers. Here is how to install it, set the depth, test the volume, and remove it without damaging the core.
Quick answer
Fit the INS-RS9D-K into the muffler outlet, seat it fully and squarely, then ride and measure before deciding whether to keep it in. It fits all RS-9 and RS-9T mufflers, but the actual decibel drop depends on the application, so treat the first ride as a test rather than a guarantee.
What the insert changes, and what it does not
The insert is a low-volume kit for RS-9 and RS-9T mufflers. It is not a spark arrestor, so do not rely on it where a spark-arrested muffler is required. That distinction matters on public land and at venues that check for an approved arrestor rather than a sound level.
Because the decibel reduction depends on the application, the same insert can sound mild on one bike and barely different on another. Use Yoshimura's insert chart to confirm the expected result for your specific machine before you buy, and plan to verify with a meter rather than by ear alone.
When to leave the insert out
If your track or trail system only checks for a spark arrestor, this kit is the wrong tool. If your muffler has impact damage or a loose core, fix that first; an insert will not correct a rattle or a leak at the joint.
Riders who want the loudest possible note should skip the insert entirely, but they should also check local noise ordinances before assuming a stock RS-9 or RS-9T will pass a sound check.
Step-by-step: install, test, and remove the insert
- Let the exhaust cool completely: Work on a cold muffler only. Touch the outlet with a bare hand before starting; if it is warm, wait. Common mistake: pulling the insert while the muffler is still hot and burning a glove or fingers. Cold metal is the checkpoint before any tool goes in.
- Inspect the outlet and the insert: Check the muffler outlet for carbon buildup, dents, or a loose core, and confirm the insert is clean and straight. Common mistake: forcing a dirty insert into a carboned-up outlet and jamming it. If the outlet is damaged or the core is loose, stop and repair the muffler first.
- Seat the insert squarely: Slide the insert into the outlet by hand, keeping it aligned with the bore. Do not hammer it. Common mistake: driving it in at an angle, which distorts the insert and makes removal hard. It should go in with hand pressure and sit flush, not proud on one side.
- Confirm the fit and retention: With the insert seated, check that it cannot be pulled out by light hand pressure and that it does not rattle when you tap the muffler lightly. Common mistake: assuming a press fit is enough without checking. If it moves freely, stop and confirm you have the correct insert for the outlet before riding.
- Test the volume before you commit: Start the engine and let it idle, then blip the throttle. If you have access to a sound meter, measure at the same distance and angle you used before fitting the insert. Common mistake: judging by ear in a garage, where reflections make the result unreliable. Compare before-and-after readings from the same spot, not from memory.
- Ride and recheck: Take a short ride, then let the exhaust cool and check that the insert has not moved. Common mistake: skipping the recheck and losing the insert on the trail. Any movement after the first ride means the fit is wrong; do not keep riding it.
- Remove it safely when you want the volume back: On a cold muffler, grip the insert and pull straight out. If it is carbon-locked, use a soft-jawed puller or penetrating solvent rather than prying with a screwdriver. Common mistake: levering against the muffler outlet and bending the end cap. Pull straight, never pry sideways, and clean carbon from the outlet before refitting.
Product facts
- SOUND INSERT KIT RS-9/RS-9T Mufflers, 1.250" dia. (INS-RS9D-K): The INS-RS9D-K is a low-volume insert kit that fits all RS-9 and RS-9T mufflers and is non-spark arrested. One kit covers multiple bikes, but it will not satisfy spark-arrestor requirements.
SOUND INSERT KIT RS-9/RS-9T Mufflers, 1.250" dia. (INS-RS9D-K)
