Yoshimura · RS-12
The Yoshimura SOUND INSERT KIT RS-12 Muffler, 1.625" (INS-31-K) is a replacement low-volume insert kit designed for RS-12 mufflers. It is intended for riders who want an optional sound-reduction setup where different sound restrictions may be required, with decibel reduction varying by application.
This kit is listed for Harley-Davidson Pan-America 2021–2022, Honda CRF250R 2025–2027, Honda CRF250RX 2025–2026, Honda Transalp 2024–2026, Kawasaki KX250F 2025–2026, Kawasaki KX250X 2025–2026, Triumph TF450 2025–2026, Triumph TF450-C 2025–2026, Triumph TF450-E 2025–2026, Triumph TF450-X 2025–2026, Yamaha WR250F 2020–2023, Yamaha YZ250F 2019–2026, and Yamaha YZ250FX 2020–2023 (see the fitment table below).
Built as a replacement low-volume insert kit for Yoshimura RS-12 mufflers, this setup is aimed at applications where a quieter configuration is preferred. Yoshimura notes that decibel reduction depends on application, so results will vary by the specific model and configuration listed in the fitment table.
This insert kit is specified as non-spark arrested. It is intended as an optional kit for applications that may require different sound restrictions, making it a straightforward service-part choice when configuring an RS-12 muffler for the rider’s needs.
The kit includes a low-volume insert tube along with an end-cap collar and a set screw. These components are provided as a matched insert assembly to support proper installation into compatible RS-12 mufflers, with an installation PDF available on the product page.
Sound
Part of Yoshimura’s Replacement Service Parts line for the RS-12 series, the INS-31-K is positioned as a practical solution for riders servicing an existing RS-12 muffler or setting up an optional low-volume configuration. It is described as a replacement low-volume insert kit intended for situations where different sound restrictions may be required, keeping the focus on adjustability through an insert change rather than replacing the full muffler.
Fitment
Yoshimura identifies this kit as a low-volume insert option, with decibel reduction dependent on the specific application. Because it is non-spark arrested, it is important to match the kit to the intended use and the correct RS-12 muffler application. The product page references using an insert chart to confirm fitment for a particular application, alongside the fitment table shown below.
Installation
Fitment is provided for a defined list of models and model years, including Harley-Davidson Pan-America 2021–2022, multiple Honda, Kawasaki, Triumph TF450 variants, and Yamaha WR250F, YZ250F, and YZ250FX model ranges as listed on the page. An installation PDF is available on the product page to support correct setup, and the insert chart reference can help confirm the appropriate application before installation.
| Part Number | INS-31-K |
|---|---|
| Brand | Yoshimura |
| Product Line | Replacement Service Parts |
| Series | RS-12 |
| Shipping Weight | 1 lb |
| Barcode | 00840025910584 |
| Make | Model | Model Years |
|---|---|---|
| Harley-Davidson | Pan-America | 2021–2022 |
| Honda | CRF250R | 2025–2027 |
| Honda | CRF250RX | 2025–2026 |
| Honda | Transalp | 2024–2026 |
| Kawasaki | KX250F | 2025–2026 |
| Kawasaki | KX250X | 2025–2026 |
| Triumph | TF450 | 2025–2026 |
| Triumph | TF450-C | 2025–2026 |
| Triumph | TF450-E | 2025–2026 |
| Triumph | TF450-X | 2025–2026 |
| Yamaha | WR250F | 2020–2023 |
| Yamaha | YZ250F | 2019–2026 |
| Yamaha | YZ250FX | 2020–2023 |
Fitment as listed by Yoshimura for part number INS-31-K.
Instructions / What's Included (PDF)
Provided by Yoshimura. Opens in a new tab.
