The REC MX Seat Nuts are designed to be an OEM replacement and use the OEM bolts. Chances are if you have a Kawasaki you already have stripped out the threads on the OEM nuts as they are just too soft. The REC Seat Nuts take a little work to fit/press into the rear fender, but once inside the chances of you stripping out or losing them like the stock nuts are slim. The nuts are $29.95 a pair (kind of expensive), but have eased our mind about possibly losing a seat on the track. No one wants to ride back on the track to find their seat and take that ride of shame through the pits. Grab your balls and get some seat nuts! You can go to RECMX.com and check them out.
Yoshimura RS-12 Stainless Muffler System (2021 Kawasaki KX450)
The stock 2021 Kawasaki KX450 is pretty damn good machine, but that muffler looks atrocious right? We called up on Yoshimura to see if we can get a more attractive aftermarket muffler system that is actually better than the stock system. I will say that the stock KX450 muffler system works pretty damn well, but as always we are constantly looking to try aftermarket pieces because as we all know, you are only as good as what you try!
The Yoshimura RS-12 Stainless System is made in the USA, is rubber mounted to the subframe, its asymmetrical shaped muffler allows maximum capacity and incorporates a resonance chamber for managing sound and increasing usable power, the unique shape also provides more clearance for tire and brake caliper, has a new patent pending Precision Taper Fit (PTF) insert ring that can make it easy for the consumer to install and remove sound inserts as well as spark arresters, comes with a carbon fiber end cap and can be fully rebuilt with repacking kits that Yoshimura sells. If you’re looking to lose a little weight with the muffler, you will have to look towards the titanium system. The stainless system weighs in at 9.12 pounds, which is slightly heavier than the stock muffler, that comes in at 9.1 pounds. We aren’t necessarily looking to lose weight in this instance, as power, sound and reliability are more important to us with this unit.
The stock muffler system is pretty damn good, as the power character of the KX450 is long and linear, but the stock KX450’s engine character could use a little more pulling power and more mid rpm response. Installing the Yosh RS-12 was painless enough and we really appreciated the rubber sub-frame mount that the Yosh muffler comes with. Having a rubber mounted rear muffler mount helps avoid the sub frame tab breaking off due to solid mounting. Once on the RS-12 is visually still big looking, but the RS-12’s exhaust note is so much better to the ears that we lost focus on how big the RS-12 looks. Out on the track we noticed how much easier the KX was to corners because there was less on/off feel from the engine on low RPM because the Yosh builds power a little more smoothly between 5000-7000 RPM. The RS-12 is less touchy to the riders throttle hand and to me that helped calm the chassis down in area 2-3 of corners. You will not get as much throttle response from the RS-12 as you do a FMF or a stock system, but to me this is a good thing. The mid range pulling power is what you will come to love from the Yosh system. Pulling power out of corners is noticeably better than stock and the rider can shift into third earlier without having to use the clutch in order to get the engine to recover (back into the meat of the power). Rear wheel traction was also an improvement on hard pack tracks as the KX450 had a better second gear flat corner sensation to the rear wheel than the stock system. Top end feels as good as stock with maybe a little more over-rev, so if you’re a little lazy the RS-12 can help you slightly in that area as well.
If you’re looking for a more explosive rpm response from your KX450, the RS-12 may not be the muffler you want to go with, but if you want added pulling power out of corners as well as more rear wheel traction with a better exhaust note, then this Yoshimura RS-12 stainless system for your KX450 is a great buy. The benefit about stainless steel is that the overall construction of the muffler will last longer than titanium. Most of my practice bikes over time had stainless systems on it for the sake of durability. Slip fit titanium joints just don’t last as long as stainless. For $850.00, the RS-12 system is a good buy with quality construction that you expect from Yoshimura.
FMF 4.1 RCT Muffler With SX Style Megabomb Headpipe (2020 KX450)
The Kawasaki KX450 was the most improved 450 machine of 2019 and with Kawasaki not changing anything on the 2020 KX450, I wanted to test some new aftermarket parts to see if I could improve on what I already knew from last year’s machine. I knew FMF had two headpipes available for the KX450, but until recently I wasn't able to try it. The SX Style headpipe comes down like a “lowboy” headpipe and increases the length in order to shift the power character around. So what exactly did the “SX Style” headpipe do to the KX450 and how is it compared to the MX Style headpipe? First let us tell you about the stock KX450’s power character.
The stock power curve of the 2020 KX450 engine has a snappy throttle response from 0-10% throttle opening (with a free feel to it) and at times can almost be too touchy through corners with the standard green coupler installed. Once rolling on the throttle and passed the corner, the power is not quite as strong as the Honda or Yamaha, but still creates an easy to ride power feel on the track. I didn't necessarily need more rpm response with the 2019 KX450, but I would be lying if I said I couldn't use more bottom and mid range puling power when coming out of corners. If you go back and read my review of the MX Style FMF Megabomb headpipe with 4.1 muffler from 2019 (https://www.keeferinctesting.com/offroad-testing/2018/8/14/fmf-41-rct-titanium-muffler-system-2019-kawasaki-kx450) you will read that the MX Style Megabomb smoothed out the low end power delivery more than the stock muffler system did, but had more mid range meat, which was noticeable immediately. In a perfect world, I would love to get more of that newfound mid-range “meat” (that the MX Style and FMF 4.1muffler system brings) and shift some of it towards the bottom end. This is why my curiosity lead me to this FMF “SX Style” headpipe.
As far as bolting on the complete system, it really is a painless install. The 2020 Kawasaki is the lightest Japanese bike in stock form, but when FMF sent me the full titanium system, I was surprised it dropped the Kawasaki’s weight by 2.4 pounds! Also this is just my opinion, but the titanium FMF 4.1 system is one of the most stunning aftermarket mufflers you can put on any bike. I love the blue anodized finish against the green plastic and it makes the whole bike pop more!
Comparing The FMF SX Style Headpipe To The MX Style FMF Megabomb Headpipe:
So how do the two headpipes with the FMF 4.1 RCT muffler compare to each other on the track? The SX Style headpipe, along with the 4.1 RCT muffler made the KX450 feel more playful out of corners than the MX style megabomb that I tried on the 2019. The low end RPM response (0-10% throttle opening) was slightly less with the SX Style headpipe (without the muffler insert), but now the KX450 had slightly more bottom end pulling power without sacrificing that extra mid-range that I liked so much from the MX Style Megabomb headpipe/4.1 muffler system. You will get slightly less pulling power on top end/length with the SX Style headpipe, but to me it was a minimal loss. Some less sensitive riders may not feel the loss of top end pull with the SX Style headpipe, but it’s something that should be noted. I prefer the SX Style headpipe on most motocross tracks simply because the KX450 pulls harder out of corners and I can shift to third gear sooner with the SX Style headpipe.
Insert in…
You want to know a tip? Don’t throw out that insert that comes with your FMF 4.1 muffler system! Why? Because I actually liked the SX Style headpipe/4.1 muffler system better with the insert in. Why? Because it gave the muffler some added back pressure and gave me some added RPM response without sacrificing a lot of mid range pulling power. With the insert in the muffler, the KX450 now has increased (0-10% throttle opening) low RPM throttle response that I was missing through mid corner and had better corner exiting power. With the insert in you also will get more connection to the rear wheel and more traction when the track gets firmer. The sound of the 4.1 muffler with the insert in is also more pleasant and isn't as loud as the larger opening of the FMF 4.1. NOTE: Not all bikes respond to inserts/back pressure the same so just know that each bike is different. If you feel like you may need a little more low end throttle response from your FMF 4.1 muffler system, try the insert.
It’s tough to get more horsepower, added connectivity, as well as an overall better engine character than what a stock exhaust can give, but FMF did a good job with the 2020 Kawasaki KX450 SX Style headpipe/4.1 RCT muffler. It retained the stock system’s low end RPM response, while getting some added bottom end pulling power, as well as mid range meat coming out of corners. In order to get the SX Style headpipe when you order, you must order the SX Style headpipe separate and use the 4.1 RCT slip on. If you order the full factory 4.1 RCT system you will be getting the MX Style headpipe. The SX Style headpipe costs $349.99 and the 4.1 RCT slip on will run you $549.99. The FMF 4.1 RCT muffler also comes with a mounting bracket for the subframe tab to ensure that the tab will not break or crack. Overall, I think this is a good upgrade to your 2019-2020 K450.
If you have any questions about this test please feel free to contact me at kris@keeferinctesting.com. I can guide you through any questions you may have.
Yoshimura RS-4 SS/AL Full Muffler System For 2019 Kawasaki KX450
By: Dominic Cimino
Any of you that stay up to date with us here at Keefer Inc. are aware that I really enjoy riding the 2019 KX450. Like I really enjoy it. Maybe it is because we have the chassis and suspension dialed in just for me or maybe it’s just because the bike is so damn fun. Either way, I am excited to continue making improvements to this bike in the upcoming months because every time I ride it I feel faster. Next on the chopping block is the motor department and we decided to start with exhaust first. I wanted to test the RS-4 Stainless Steel Yoshimura system because I have had great luck in the past using their systems on other bikes and the guys over there always take great care of us.
Yoshimura exhaust systems are made from scratch right here in Southern California. Their R&D facility houses everything from the race team shop, dyno/engine rooms, to the space where they lay all of their own carbon fiber. The attention to detail and quality of product is top notch in everything they produce and to give you a little more background on Yosh, you can watch this short clip:
https://www.youtube.com/watch?v=V5J5kltNfvQ
Although it is a couple years old and mainly showcases road racing disciplines, trust me when I say that it all translates equally into motocross. You can sleep peacefully knowing that your investment is going to be worth it.
The stock exhaust system on the 2019 KX450 is not too bad overall. Beside it looking really bad (that is a no-contest) and weighing a decent amount, it produces a good tone and useable power. I think this exhaust compliments the motor and power delivery well by keeping things linear and quick revving - one of my favorite traits about this bike overall. But on the flip side, the motor does lack some “meat” in the RPM range and the over-rev tends to sign off relatively quickly at the top. Installation of the new Yosh was quick and easy with every single piece fitting in place perfectly. I love when that happens! The stainless/aluminum system that I tested weighed over a pound less than the stocker and comes in at a fair price of $675.78. In roughly ten minutes, the KX looked better instantly with the new system in place, and when I pushed the button to wake her up, she sounded healthier too. I am not a fan of obnoxiously loud exhaust systems so I was happy to listen to the Yosh when cracking the throttle on the stand. Definitely louder than stock, but not deafening.
Before installing the new Yoshimura system, I did a couple morning motos at Glen Helen to get the best gauge of the stock comparison. The most obvious difference when cruising back onto the track was the tone, as it has a deeper/healthier sound. But when in stride, the exhaust made the KX come to life from the mid range and beyond. The linear power curve stayed true on delivery, but exemplified a more crisp powerful feel when on throttle. I felt the Yoshimura system was able to harness a little more “meat” that I have been searching for and also helped push the bike into the higher revs more efficiently. On the top end, over-rev was increased quite a bit as the KX seemed to pull longer and harder overall. I noticed when charging down Mt. Saint Helen I could hold 2nd gear almost half way down the hill before hitting the limiter. The stock exhaust would sign off way earlier than that in the beginning part of the day. I also realized I stayed in 2nd gear almost all the way around the Glen Helen circuit. This is a testament to the linear power I have been talking about on this 2019 KX450, and the Yoshimura system makes it even better. Where I didn’t notice a substantial improvement was bottom end power delivery. The KX is not a torquey bike in stock trim by any means, but I was expecting to get a little more bark with the new system. This was not the case and I found myself clutching the bike in the soft corners to wake it up in order to get back into the mid range, where I think it excels.
Overall, the new Yoshimura exhaust system is a great performance improvement to this already great bike. Looks good, sounds good, and runs good - thats what it’s all about, right? Obviously, I am going to set my sights on continuing to improve the power delivery to round out this new KX450. I am happy with the mid/top end feel, so maybe we can experiment with new map settings to get a little more lovin’ down low. As always, stay tuned for what is next here at Keefer Inc. If you have any questions about the 2019 KX450 please feel free to email me at dominic@keeferinctesting.com. Or you can head over to Yoshimura-rd.com to see what they offer for your green machine.
FMF 4.1 RCT Titanium Muffler System (2019 Kawasaki KX450)
The 2019 Kawasaki KX450 is the most improved machine of the new year, hands down! It has a very responsive engine character, comfortable suspension, a lightweight feel and cornering that is very neutral. I will be the first one to admit that I get nervous about sticking on any type of aftermarket muffler system when I really like the stock power curve of any machine. Sometimes aftermarket mufflers are just smoke and mirrors. They are lighter, titanium, look cool, but in the end they are no better than your heavy, ugly, big stock muffler. While I was testing the 2019 KX 450 earlier this year I could hear this little voice inside my head say “it’s going to be tough to make a muffler that is better than this stock one”. Fast forward to a few weeks ago and a shiny new FMF 4.1 RCT titanium exhaust shows up at my door, to be evaluated on the green machine. I sat on it for a week knowing that this new, shiny, lightweight piece of FMF artwork might not be better than the current monstrosity that is on the 2019 KX450. Nonetheless I installed the FMF system (which was easy I may add) and headed to the track to give it a go.
The stock power curve of the 2019 KX450 engine has a snappy throttle response (with a free feel to it) and at times can almost be too much through corners with the standard green coupler installed. Once rolling on the throttle and passed the corner, the power is not quite as strong as the Honda or Yamaha, but still creates a easy to ride power feel on the track. I didn't necessarily need more rpm response with the 2019 KX450, but I wouldn’t mind some more meat through the mid to top end range. Bolting on the KX450 FMF Factory 4.1 RCT system is by far the easiest system I have installed on any 2019 machine. Installation literally took me through two full songs on the “Classic Rock” station on Pandora. Not bad! The 2019 Kawasaki is a light bike stock, but FMF sent me the full titanium system, which dropped the Kawasaki’s weight by 2.9 pounds from the stock system! To me the titanium FMF 4.1 system is one of the most stunning aftermarket mufflers you can put on any bike. I love the blue anodized finish as it looks good on almost every make and model machine there is.
FMF builds great looking mufflers!
On the track the FMF 4.1 makes a slightly smoother bottom end power delivery, but keeps that exciting RPM response. Where most of you will feel your hard earned money is in the mid range pulling power when exiting corners. The stock system feels empty in this area, but the FMF fills in the power through the mid-range. What I mean by “fill in the power” is that the FMF system actually feels like it is shooting forward, as soon as you shift into third gear, unlike the stock Kawasaki’s power where it lacks some “meat” through the mid-range. The FMF 4.1 increases that mid range area and gives the rider some more freedom to be lazier in third gear. That is great news for all you vet riders out there, trust me! Top end is also increased slightly and you get increased pulling power near the end of each straight with the FMF. Over-rev is slightly increased as well with the 4.1 (over the stock muffler) as I could leave the KX450 in second and third gear slightly longer. The one downside to me is that it is loud sounding (compared to the stock system). It has more of a deeper/throatier pitch to it, which makes it sound louder than the stocker.
I tested couplers along with mapping with the Kawasaki R&D guys and came up with a couple options for you (see attached maps). The white coupler map is better for bottom-mid range power, but the black coupler map is slightly better from mid to top end (the black coupler map is what I am running now). The good news is, unlike last year, the 2019 KX450 FMF 4.1 system will not have that de-cel popping with either coupler (along with these installed maps), which is a huge plus when it comes to a clean ignition/fuel mapping power feel.
Black Coupler Fuel Map
Black Coupler Ignition Map
White Coupler Fuel Map
White Coupler Ignition Map
At the end of the day the FMF 4.1 RCT full titanium muffler system delivers a smoother roll on bottom end delivery with a mid to top end puling powerl that is better than stock (along with improved mid-top end RPM response). I will say this again….Being able to achieve a power delivery that is better than what an OEM muffler system can give you is very hard to do. FMF has achieved this with their 4.1 system on the 2019 KX450. Not only does it make power, but it also takes off some weight and looks better than the stock bazooka. I wanted some added control down low and more mid range (on the 2019 KX450) so with this FMF system I got what I was looking for. I am not going to sit here and tell you guys that every FMF system, for every machine is better than stock, but with this one they knocked it out of the park. Don't be scared to try the maps that are attached above, because with today's four-stroke technology, getting the correct mapping for a certain muffler can really make a difference.
Attention mechanically inclined riders!!!!! Please note that re-packing of the FMF muffler is important for the can’s lifespan. The muffler portion (or can) will start to leave hot spots/scarring when the packing starts to burn away from inside. Once you start seeing these “hot spot/scars/markings” on the muffler, remove and re-pack it ASAP. FMF offers re-packing kits and taking the can apart to re-pack is not that hard to do. I get around 12 hard engine hours before I see these markings and have to re-pack. If you run it past the recommended time, you run the chance of hurting performance and damaging the core (or perf) inside the muffler. Don’t be a dummy and waste your money, re-pack your muff!
If you have any questions about this test please email me at kris@keeferinctesting.com
2019 Kawasaki KX450 Clutch Mod
Do you have a 2019 Kawasaki KX450? If so, we are here to give you a little inside knowledge. The new 2019 KX450 is one great machine, but the doesn't mean it is perfect right? On our test bike we have experienced with some clutch drag and clutch lever movement when riding. Under heavy load (or acceleration on deeper tilled tracks) the clutch on the 2019 can drag and or the clutch lever can move. This is not something we liked, so we went to work with Kawasaki to remedy this problem.
If you are reading this and you haven't felt any of these sensations while riding then DO NOT WORRY ABOUT IT. If you do notice a drag or lever movement, simply take the judder springs and narrow fiber plate out of your clutch and replace it with a standard fiber plate (as shown). That's it! Once this mod has been installed, the lever was much more consistent and the drag we felt out of corners was gone. Not only was the drag gone, but we also noticed that rear wheel traction was increased a little as well. It's a cheap fix and relatively easy to do. Enjoy your green machine!
