When we got a hold of a 2023 Kawasaki KX250X for a long-term review, we were ready to go. Our goal was to find out how it worked as a high-performance trail bike rather than a racebike. However, a couple of things got in the way. The stock muffler lacks a spark arrester, and it’s very loud. A Fisch Moto Spark Arrestor insert got us legal, but the KX250X was still pumping out the dB. That’s fine for racing, but not great for trail riding. Fortunately, the Pro Circuit T-6 Stainless Slip-On muffler addressed both issues adroitly while providing some unexpected positive side effects.
The Pro Circuit T-6 Stainless Slip-On arrived at the Ultimate Motorcycling garage professionally packaged, with the muffler safely ensconced in a hard-cardboard tube inside the Pro Circuit box, and the mid-pipe wrapped securely in bubble wrap. The USFS-approved spark arrester was already installed. We were off to a good start.
Because I have ten thumbs as a mechanic, I got the job of installing it solo. Let me assure you that if I can do it, anyone can do it. If I can’t do it, you probably still can do it easily.
I pulled off the stock KX250X muffler—no problem there. I weighed the stock muffler, which has an integrated mid-pipe, and the result was 6 pounds, 3.5 ounces. Throwing the Pro Circuit T-6 Stainless Slip-On muffler on the scale, it hits 5 pounds, 13 ounces. Add in the 13.7-ounce mid-pipe, and the total for the Pro Circuit assembly is 6 pounds, 11.5 ounces. So, it adds eight ounces to the KX250X—a negligible amount, especially for trail riding duty. It’s worth noting here that the canister is aluminum, and the end cap is stainless steel.
Installing the Pro Circuit T-6 Stainless Slip-On muffler took me about an hour, but that’s only because I’m constantly worried about breaking something.
The mid-pipe went on without drama, increasing my confidence—something that always makes me wary of what’s next.
My initial attempt had the muffler’s mounting bracket on the inside of the KX250X’s frame bracket. As soon as I eyeballed it, I could see the Dunlop would be rubbing the muffler as soon as I hit the first bump. Obviously, I had it wrong.
It was clear that I had to get the muffler bracket on the outside of the frame bracket. Well, that wasn’t easy. I tried muscling it, but I was concerned I might bend something.
I put in an emergency text to Editor At Large Bill Kranhold. He recommended a rubber mallet. He was probably right, but I wasn’t going to start pounding on a new $591 muffler.
Throwing caution to the wind, I started gently applying some of the muscle I’ve been building at Built 45 Fitness in Sylmar. The more pressure I used, the closer I got to lining up the holes on the two brackets. Eventually, I got there! I screwed the bolt in with a Motion Pro t-handle (felt like a pro), and it was done. The tension plus the bolt gives the Pro Circuit T-6 Stainless Slip-On muffler the reassuring feeling of a rock-solid mounting.
Really, it’s a miracle that I got it done without some sort of disaster, demonstrating that installing the unit is truly idiot-proof. I took photos and sent them to my friends, completing my victory lap. Needless to say, the responses I got were generally skeptical of my claim that I did it alone.
After starting the KX250X up to make sure I hadn’t bent a valve or broken a cam chain in the process, the first blip of the throttle revealed how much quieter that Pro Circuit T-6 Stainless Slip-On muffler is than the stocker. It takes the annoying higher-frequency rasp out of the bark, leaving a pleasingly meaty rumble—exactly what we wanted. According to Pro Circuit, the muffler does not meet FIM sound standards for world competition. We were satisfied with the reduction in sound output regardless of what the FIM thinks.
We skipped dynoing the muffler because it doesn’t matter for this test. For a trail rider, it’s not about how the bike performs on a dyno with the throttle wide open—it’s all about feel. If you’re going racing, look into the Pro Circuit Ti-6 Pro Titanium exhaust system, which is more than twice the price.
Feel is always subjective; however, it’s what we do as motorcycle testers. With the nasty soundtrack subdued, the 2023 Kawasaki KX250X has a much smoother power delivery, particularly at lower rpm. The sensation is that instead of feeling a punch from each firing stroke, the power pulses blend together. The result is the feeling of better traction, reduced likelihood of stalling, and more predictable acceleration.
The mid-range and top-end remain strong—if there is any power cut, none of our test riders can detect it. If something is knocked off when we hit 14,000 rpm, we will happily trade that for more tractable power in the sub-10k range we usually ride.
The reduced sharpness of the exhaust note makes the Kawasaki KX250X less fatiguing to ride. Also, riders behind the PC-muffled KX250X noted that it was no longer annoying to be right behind it.
In addition to the real-world performance enhancement, the Pro Circuit T-6 Stainless Slip-On muffler looks great. The build is high-quality with top-notch TIG welding, and the aluminum mounting bracket looks trick. The Pro Circuit logo, recognized motoworldwide, is proudly displaced on both sides.
The Pro Circuit T-6 Stainless Slip-On muffler ended up doing more than we expected. We were looking for a USFS legality at the very least, and we got that. The bonuses were smoothing the power delivery at lower rpm and reducing the raspy sound—two pleasant surprises. It’s great to be able to go legal and get a robust product that works better at the same time.
Action photography by Kelly Callan
Pro Circuit T-6 Stainless Slip-On Muffler Review Photo Gallery
