Yoshimura · RS-12 · Full System
The Yoshimura RS-12 Signature Series Full System is a stainless full exhaust system built for the Kawasaki KX250F 2025–2026 and Kawasaki KX250X 2025–2026. Developed around the latest KX250F chassis and engine package, this system is designed to sharpen rider connectivity and deliver stronger output across the power spectrum.
It ships with the INS-31-K sound insert installed, chosen by Yoshimura for an ear-pleasing exhaust note and the best power on this application. For riders who head off the track, an SA-21-K spark arrester is also available separately; see the fitment and insert/arrester information on the page for details.
Materials
Yoshimura’s Carbon Faced Machined Joint is designed to eliminate the need for anti-seize. By impregnating the surface of the stainless steel joint with carbon atoms, friction is reduced to help decrease wear over the life of the joint, supporting consistent fit and long-term serviceability.
Technology
An integrated header resonator is engineered for more than appearance. Yoshimura uses this feature to help maximize power across the spectrum while enhancing rider connectivity, contributing to a more usable, responsive feel through the bottom, mid, and top of the rev range.
Included
This RS-12 system comes with the INS-31-K sound insert installed. Yoshimura selected it to produce an ear-pleasing exhaust note and to deliver the best power for the new Kawasaki KX250F application, making it a ready-to-run setup right out of the box.
Performance
With the latest KX250F featuring a new chassis and engine package, Yoshimura developed the RS-12 specifically to add performance to the updated platform. As a Signature Series Exhaust System, it’s positioned as a focused, application-specific full system for riders who want a more connected feel across the powerband on the 2025–2026 KX250F and KX250X.
Engineering
Yoshimura reports verified gains of “up to 3.3% more HP at 11” and “up to 3.4% more torque at 10” with this RS-12 full system. Combined with the system’s development notes, the goal is added strength up top along with improved connectivity through the bottom and mid portions of the power spectrum.
Sound
The system is supplied with an INS-31-K sound insert installed, and additional options are offered for tuning sound and use-case preferences. An INS-39-K sound insert is available separately, and the SA-21-K spark arrester is also available separately for riders who plan to venture into the woods. Refer to the sound insert and spark arrester table shown on the page for the available codes and what’s included.
Figures as reported by Yoshimura.
| Part Number | 242950S521 |
|---|---|
| Brand | Yoshimura |
| Product Line | Signature Series Exhaust System |
| Series | RS-12 |
| System Type | Full System |
| Material | Stainless |
| Sound Insert (Included) | INS-31-K |
| Spark Arrester | Not included |
| Shipping Weight | 18 lb |
| Barcode | 00840025919976 |
| Emissions Compliance | QUALIFIED MANUFACTURER DECLARED "REPLACEMENT PART" |
| Make | Model | Model Years |
|---|---|---|
| Kawasaki | KX250F | 2025–2026 |
| Kawasaki | KX250X | 2025–2026 |
Fitment as listed by Yoshimura for part number 242950S521.
| Part Number | Type | Included With This System |
|---|---|---|
| INS-31-K | Sound Insert | Yes |
| INS-39-K | Sound Insert | No |
| SA-21-K | Spark Arrester | No |
Instructions / What's Included (PDF)
Provided by Yoshimura. Opens in a new tab.
