Pipes on two-strokes were a must-have just a few short years ago. But the stuff coming stock has slowly become really good, especially from KTM. This forced FMF back to the drawing board on a number of its KTM pipes and specifically on the 150 SX. Although the KTM 125/144 pipe would work just fine, the two-stroke expansion-chamber-heads at the Flying Machine Factory knew there was a bit more to be had, even when put against a stock pipe and muffler that are tough to beat.Well, I put the combination to the test, and I need every ounce of power I can get out of that little screamer for my 185-pound chassis. The fit was spot-on, and it took less than 10 minutes to switch out the pipe and muffler. The muffler now includes the rubber grommets, and the pipe has O-rings already installed. The first thing we noticed was a crisper sound out of the slightly shorter muffler. It was just a tick louder to the ear than the quiet stock muffler through the rev range, yet was still under 96 decibels in the 20-inch test. It did not make the bike offensive like a shorty muffler would and was plenty respectable even considering the sound of the two-stroke does not carry like a thumper’s does. The power increase was a little harder to feel but was definitely there. As a combination, the FMF setup gave the KTM a little more hit on the bottom, slightly better pull in each gear and just a smidgen more power on top.
This does not sound like much, but as highly tuned as this bike comes, it is difficult to get even small improvements without any sacrifices. Where you can tell is in loamy, high-traction times where the bike is way easier to keep on the pipe. Also, jumps that are hard to clear get a little bit easier from the increased oomph. There are no sacrifices with this system. I tested the pipe with the stock muffler and the FMF muffler with the stock pipe, and neither mixed combination was as good as stock and certainly not as good as the FMF combo. The only issue I had was with the FMF O-rings getting cooked and breaking. I’d simply throw on some stock KTM ones instead, and FMF is already addressing the issue with updated O-rings. The little boost in performance would certainly be enough to get me interested in this pipe and muffler, but it is especially reassuring to know that when your stock pipe gets dinged up, there is a better one waiting when needed. -Jimmy Lewis