MXA TEAM TESTED: FMF RACING’S 2025 YAMAHA YZ250F SLIP-ON MUFFLER

WHAT IS IT? The Factory 4.1 titanium exhaust system is FMF’s top-of-the-line option for slip-on systems. With a shorter overall length than the previous generation, the Factory 4.1 muffler is less susceptible to crash damage. The latest Resonance Chamber Technology (RCT), both internally and externally, brings the product that you can buy closer to what the factory teams use.

WHAT’S IT COST? $849.99 (slip-on). 

CONTACT? www.fmfracing.com or (310) 631-4363.

WHAT STANDS OUT? Here’s a list of things that stand out with FMF Racing’s Factory 4.1 slip-on muffler for the 2019–2025 Yamaha YZ250F models.

(1) Aesthetics. The FMF system will give your Yamaha that factory look right out of the box. When you get the titanium slip-on, it comes with a blue anodized muffler that matches the look of the blue plastic nicely. Getting rid of that big and bulky stock muffler is also a plus. 

(2) Performance. Although the stock muffler is 3 pounds heavier than the FMF muffler, it is no secret that it’s very hard to beat the performance of the stock muffler. Even if the muffler has a horrible sound, the Yamaha R&D crew did come up with a strong exhaust. So, how did the FMF compare to it? Off the initial crack of the throttle, test riders felt that the FMF and stock system were the same. Where the FMF slip-on muffler shines is in the mid- to top-end range. The FMF gave the YZ250F more pulling power to the rev limiter without falling flat. This allowed our riders to stay in a lower gear longer and not have to shift as quickly on straightaways. Comparatively, with the stock system, the power would fall flat on fast straights if the riders didn’t grab the next gear quickly. 

(3) Durability. We have about six hours on our FMF Factory 4.1 slip-on, and the packing is holding up nicely. Despite a couple of tip-overs, the only thing to suffer damage so far is the sticker. The sound of the FMF muffler should also be considered when deciding between your options for power-producing YZ250F upgrades. The stock muffler is obnoxiously loud with the worst-sounding muffler exhaust note in the 250F class. The FMF muffler fixes that. 

(4) Installation. FMF has been known for its spot-on fitment throughout its entire line of exhaust systems. The Factory 4.1 slip-on is no different. To install the muffler, you will need to remove the right-side number plate and the three bolts holding the stock system on. You will also need to remove the rubber bushing and metal collar on the stock system, and install them on the FMF. Also, the FMF system doesn’t require the clamp that holds the stock muffler onto the mid-pipe.

WHAT’S THE SQUAWK? It’s not cheap.

MXA RATING: The FMF slip-on provides more midrange and top-end power, and it sounds 10 times better than the stock system. It transformed our stock YZ250F into a race bike.