*UPDATE* I rode a buddy’s bike & I’m questioning EVERYTHING

I don't think I've seen anyone say the SFF is good suspension lol

 Not a lot of tuners have a good setup for that fork. The ‘17 engine was weak sauce but could get the job done.

Right lol! I've sworn off 450's in my advanced age and have been on a 350 for a couple years now. A friend of mine just got a '25 Blu Cru 450. Something about the Yamaha's just appeals to me so much. I told him, "I'm riding this thing next week." This was a couple weeks ago. I won't do it. I'm afraid I'll like it to much. I know it's too much motor for me but I'm really drawn to riding the Yamaha chassis and suspension 

Get with me at a practice and we will let you ride one of our 450's, see what you think!  

Wow! It would take me 5 weeks to get in 78 laps. 🤣

The bit of time I've spent on SFF forks was not terrible, but definitely nothing to write home about. 

My '21 MC450F came with air forks, raced with them for two years. They were not bad, but had a weird dead spot in the middle of the compression of the fork - most noticeable in the turns, you kind of just lose front end feel and the result was not being able to feel the tire push or lose grip. Outside of that, no real complaints there besides checking air pressure often....when the sun comes out they'd go up in pressure.

Now, I've got MXTech Raven inserts in the forks, and the rear shock redone with bladder kit, all valved [normal stuff]. Completely different motorcycle after that. I've never had suspension this nice before, but man is it amazing now - tracks perfectly straight coming into rough chop, almost to the point it gives you too much confidence. I just check my sag fairly often and bleed the forks, and off I go.  

Also I wanted to point out the 450 being too fast thing, I actually re-geared my bike based on Keefer's recommendations and it's made a world of difference for me. 14-52 if I recall correctly, final drive ratio being a 3.71 versus the stock 3.77. Now, this bike was never known for arm ripping torque but it smoothed everything out and the longer ratio makes it so you don't have to shift so dang much. I wouldn't recommend it on a 250F, but the 450 has plenty of torque to get you through/over stuff.  

I put a 6500 kit in my 19 xcf. It  is amazing and I would recommend trying one. 

Suspension fluids are no different than motor oils and after 10 hours suspension fluids start breaking down and thinning and at 36 hours a simple suspension service with fresh fluids will feel like it was revalved. These fluids are part of lubricating internal parts so broken down fluids will cause wear affecting performance too.

So now we got to decide between a 24/25 YZ250F or KX450?! 😀

I’m also a vet C rider, three years ago I rode a buddy’s 2020 yz250f and loved it immediately. It felt planted and stable everywhere and soaked up everything. I got back on my 2016 KTM 250sxf and thought that I couldn’t let myself be better on his bike or all I would be thinking about was getting a Yamaha. Next moto back on my bike I wasn’t as comfortable but tried to push through where I was more comfortable on his yz. I lost it on lean angle with some chop going up the face of a jump, got thrown, lights out with a bunch of broken bones. I came back a little over a year later and he sold me his yz and I’m still loving it!

I’d say go with what you know that you feel most comfortable with rather than trying to push through something else.

You have had your first bike set up epiphany! Welcome to the dark side!

Not all bikes are created equal, not all mods make your bike better. The stock Yamaha 250/450 for the last 6 years have been unbelievable out of the box. That’s why they are winning so many bike tests.

In my opinion you aren’t just feeling the suspension difference but the the frame bump compliance, the bar flex, could be better tires… there’s many things that make that Yamaha better to me on paper than the Kawi.   

Don’t be scared to sell your bike and get a Yamaha. It would be almost impossible to get your Kawi to feel that same way.

I love my Yamaha 450 but it is a lot of bike. I’m 185lb and still trying to tame the power down. Must have is the mellow Vortex from Twisted development.

The Kawi 450 is an amazing bike and much easier to ride power curve. I think the chassis and suspension comfort are similar. If you asked me, I’d suggest the Kawi. They are crazy good deals right now also. I think the Yamaha 450 might be too much bike for where you are at right now.  

The Yamaha 250 is amazing, not sure why that’s not in the running?

I think by all accounts a 2019-2024 YZ250f is going to pull harder than the 2016 you test rode. It won't be quite as stable but a 450 won't be either.

A YZ250 with the HITLIS powervalve kit makes for a more stout PB yet smooth as you want that mid YAT to be. According to a buddy, saying feels more 300-ish.

KYB PSF1 A-kit forks set up correcty can.

And I am talking in comparison to KYB A-kit spring forks, not just standard issue KYB SSS forks (which are amazing).

An interesting data point:
When I was putting together a 2016 YZ250F big-bore bike ---> One of the national MX race Dads I consulted with regarding what configuration to go with said "we're not sure why, but the 2014-2018 YZ250F motor always ended up being higher output and more reliable."

Anyone know why this is?

You just experienced a suspension that is perfectly tuned to you. From here forward you will judge every suspension against this experience. I know. I fell in love with a buddy's 94 RM125 a long time ago for the same reason. It felt like the harsher the impact, the plusher it got. Within a lap I was fearlessly tackling braking and acceleration bumps, whoops and flat landings like they were nothing. My YZ would punish me on the same stuff. Never felt anything so perfect, even to this day. He said his setup was stock. I was ready to junk my YZ. Then I got hurt a little and he went arenacross racing.

Owned a 12, 14, 16, 18, 19, 25 YZ250F, all the things you highlighted OP are what makes that bike amazing, so many neigh sayers when it came out in 14 and has just been tweaked and perfected since. The 24 imo of owning a few gens was the best, slim feeling, better turning and handling and still had enough bottom end and the supsension, basically the whole package. Right now theres $750 cash back, promo financing and seeing some left overs for $6800 range. Id make the jump if you are feeling the itch as you said it made you a better more confident rider. 

In 2017 I was riding a '17 KTM 250f and I hopped on my friends 2017 KX 250, and my god, that bike felt so harsh.  Absolutely hated the feel of the forks, chassis itself was pretty rigid too.  The SFF forks are nearly as bad as the WP 4cs forks IMO.

Had a set of those on my SX150, trash. 

When you listen to podcast with Keefer and Rikki Gilmore - Rikki stated they didn't know enough about its potential and believes it could be allot better and has more potential than spring.

The SFF being discussed here is a spring fork. The TAC fork is better but takes a bit of talent to dial in.

Dude the 2011/2019 KXF 250 forks are terrible, they are Showa’s SFF (single spring) and they never got them right. I had a 2011/2014/2019, when I jumped on my old 2021 and now on my 2023 the difference was night and day difference. From 2020 they used the same forks and shocks as yamaha’s, just different valving and i’m really liking them.

Kawi is always pretty “hard” on the valving, you need to be 65/70kg and be pretty fast to get them work as they should.

Just get a newer bike, your 2017 is 8 years old. 

I’m unbiased and firmly in the pumpkin patch. However just from reading through all this it sounds like you like the YZ but you’re trying to talk yourself into staying on the KX. 
Trouble is. The heart wants what the heart wants. 
Go get the YZ. 
You’ll be happy you did and it will be one less excuse in your head when you suck on race day!

Good luck 🤞 

Just reading OPs title I expected this to be an After Dark thread.

I’m some what of a suspension nerd, built my own shock vacuum bleeder, started with race tech gold valves in the 90s and now revalve on my own… so to say the fresh fluid with bushings and seals made a big difference doesn’t surprise me at all! I change fluids every 10 hours and seals and bushings at 20! That being said… if you like the YZ i can assure you your KX with SFF will never perform like a YZ, just get one, you only live once and you can’t take the money with you! 

Years ago, I went to a KTM ride day to try out the SX450. I was racing a YZ250 two stroke at the time (I said it was years ago). Off road superhero Larry Roeseler was helping the local dealer run the show, and when I signed up to ride, all the demo bikes were out on the track. So Roeseler let me ride his personal bike. He had already retired by that point but he still rode regularly and he had a super trick 450. I jumped at the chance!

Now, I was way bigger than Roeseler, so the sag was way off and I expected the worst as far as bottoming. But what I actually experienced was sheer magic. So plush, it was like riding on a cloud, but it was totally stable and never bottomed… although admittedly I was taking it easy on the King of Baja’s personal ride! What really stuck out was how well it handled. We were out in the California desert, and conditions were dry and hard pack, but Larry’s bike cornered effortlessly and even when the rear did step out, it was completely controllable. I was doing feet-up powerslides with ease, something I never did on my YZ. 

My point: riding someone’s professionally sorted bike can change the way you look at your own ride and riding, just like the OP has learned. Kudos to him for making some changes for the better.