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WHAT IS IT? The FMF Factory Fatty pipe has been a staple of FMF’s two-stroke line for many years, and FMF has pipes and silencers that fit 2005 to 2018 YZ125s. The Powercore 2.1 silencer is new technology that has joined the ever-popular and compact Shorty Powercore 2 silencer.
WHAT’S IT COST? $249.99 (Factory Fatty pipe), $239.99 (Fatty pipe), $399.99 (titanium Powercore 2.1 silencer), $129.99 (Powercore 2 silencer).
CONTACT? www.fmfracing.com or (310) 631-4363.
WHAT STANDS OUT? Here’s a list of things that stand out with FMF Factory Fatty pipes and silencers for the 2005-2016 Yamaha YZ125s.
(1) Installation. O-rings do not stand the test of time. The last thing you want to deal with when buying an aftermarket pipe is discovering that the O-rings on the old one are damaged. We applaud FMF for including fresh O-rings with our Yamaha YZ125 pipe. So, before you mount the new Factory Fatty pipe, don’t forget to install the new O-rings (even if your old O-rings look fine, we still recommend installing the new ones). The FMF pipe mounted with ease, as did the silencer, but make sure to leave all the brackets and bolts loose until you get everything in place. Since the silencers only use the bottom mount, don’t forget to put a bolt back in or the fender will not be secured. We replaced the long bolt with a shorter one so it doesn’t stick out like a sore thumb.
(2) Stock trim. For over a decade the YZ125 engine has remained the same. It was once the best production 125cc engine the world has ever seen; however, in recent years that has changed. Husqvarna’s and KTM’s latest 125cc engines can blow the measly 34 horsepower of the YZ powerplant out of the water. On the track, the YZ125 suffers the most from the bottom to the midrange. The clutch has to be abused to get the YZ125 into the meat of its powerband. To allow it to compete with the two Austrian brands, the YZ engine needs help. One of the best performance upgrades you can buy for a YZ125 is a good-performing aftermarket pipe. Exhaust pipes are relatively cheap power, and they do not directly affect the durability of the engine. We tested the FMF Fatty pipe with both the FMF Powercore 2.1 silencer and the Powercore 2 silencer.
(3) Powercore 2.1. FMF gave us two $399.99 Powercore 2.1 silencers to test to see which one would be better for them to put into production. The only difference between the two was 2-1/2 inches in length. First, we bolted on the longer one. The Factory Fatty pipe and long 2.1 silencer livened up the power across the board, but test riders found it hard to keep the power in the meat of the pocket. It still suffered down low, but perked up once we hit the sweet spot from the mid to the top. The shorter 2.1 silencer, however, made more power across the board. It was quick to respond with a power curve that never dipped throughout the range. This combination worked best.
(4) Powercore 2. We know from experience that a shorter silencer will usually produce more bottom-end power, but it has the potential to take away from the top end. The $199.99 Powercore 2 silencer has a compact design that makes it an ounce lighter than the shorter FMF 2.1 titanium package. As for performance, the bottom end produced a strong hit like the 2.1, but gave up just a little from there on up. Although we liked both silencers much better than the stock YZ125 unit, all our test riders picked the short Powercore 2.1. But when we asked our test riders if they would pay an extra $200 for the 2.1, about half the riders changed their minds.
WHAT’S THE SQUAWK? Two quibbles. (1) The price is steep for the titanium Powercore 2.1 silencer. (2) Both silencers are too short to mount with the top bracket that bolts onto the rear fender. This leaves the bolt sticking out like a sore thumb. It would be awesome if FMF included a shorter bolt with the silencer for a cleaner look.
MXA RATING: The Fatty pipe was awesome with both the Powercore 2 and 2.1 silencers. We liked the Powercore 2 for its price and the 2.1 for its potent power.