Yoshimura · RS-4
The Yoshimura SOUND INSERT KIT 94db RS-4S Muffler, 1.375" (INS-18-K) is a replacement low-volume insert kit designed for RS-4 "Turn-out End-cap" mufflers. It’s intended for riders who need an optional insert solution when an application calls for different sound restrictions, with decibel reduction varying by application.
This kit fits Honda CRF250L 2017–2020, Honda CRF250L-Rally 2017–2020, Yamaha WR250R 2008–2020, and Yamaha WR250X 2008–2011. For application-specific confirmation, refer to the insert chart and the fitment table on the page.
Built as a replacement low-volume insert kit specifically for Yoshimura RS-4 "Turn-out End-cap" mufflers. It’s a focused service-part solution meant to restore or change insert configuration without replacing the entire muffler assembly.
Offered as an optional kit for applications that require different sound restrictions. Yoshimura notes that decibel reduction depends on application, making it a practical choice when adjusting to varying riding areas or requirements.
Includes the key pieces needed for the insert setup: a low-volume insert tube, an end-cap collar, and a set screw. This combination is designed to provide the correct insert hardware package for the intended RS-4 configuration.
Sound
As part of Yoshimura’s Replacement Service Parts line and RS-4 series, the INS-18-K is designed to support RS-4 muffler owners who need a low-volume insert option for the "Turn-out End-cap" style. It targets a specific muffler configuration rather than trying to cover multiple designs, helping keep the selection process straightforward when the correct insert is needed.
Included
This insert kit is centered around the low-volume insert tube, paired with an end-cap collar and set screw. Together, these components form the insert assembly needed for the intended RS-4 setup. Installation guidance and product media are provided on the page, including an installation PDF and a product video for added reference.
Fitment
Yoshimura lists fitment for Honda CRF250L 2017–2020, Honda CRF250L-Rally 2017–2020, Yamaha WR250R 2008–2020, and Yamaha WR250X 2008–2011. Because insert fitment can be application-specific, Yoshimura also recommends using the insert chart to confirm the correct match for the muffler and application shown in the fitment table.
| Part Number | INS-18-K |
|---|---|
| Brand | Yoshimura |
| Product Line | Replacement Service Parts |
| Series | RS-4 |
| Shipping Weight | 0.5 lb |
| Barcode | 00840025908758 |
| Make | Model | Model Years |
|---|---|---|
| Honda | CRF250L | 2017–2020 |
| Honda | CRF250L-Rally | 2017–2020 |
| Yamaha | WR250R | 2008–2020 |
| Yamaha | WR250X | 2008–2011 |
Fitment as listed by Yoshimura for part number INS-18-K.
Instructions / What's Included (PDF)
Provided by Yoshimura. Opens in a new tab.
