YZ250X...the next KDX?

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bufftester
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YZ250X...the next KDX?

Post by bufftester »

Got to ride one recently, a 2023 model year, and to me it has all the right hallmarks
- more budget friendly than every other 2T out there
- Long production run with relatively minor changes
- Proven, reliable, simple motor
- competent, even if not bling worthy, frame and suspension
- lots of aftermarket support
- not orange (ok that one is just one of my tick marks)

There are things that could be done better, most notably change the 5 speed gearbox to the old WR 6 speed, put a headlight on it, add electric start (I mean EVERY other bike in their offroad line up has it except the 2Ts) although kicking it was as effortless as my KDX.

It was as much fun to ride as my hybrid, and blue is much closer to green than every other color out there :grin:
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Re: YZ250X...the next KDX?

Post by Chuck78 »

Is it possible to swap the WR 6 speed gearbox into the YZ250? My buddy with several YZ's jumped ship and moved on to Beta solely because he said he either had to gear his YZ250X for hard enduro riding, or he had to gear it for the fast sections of the hare scramble races. But neither gearing would do well in the other scenario.... He told me yesterday though that he's struggling with the longer wheelbase of the 300's in general as well as the power delivery and nimbleness... I thought he was going to get the 200RR Race Edition after we attended the Beta demo rides. I rode the 300 and thought "yeah, this is a long chassis, and the extra rotational weight of the 300 engine internals really can be felt in the handling at speed..." The H-series KDX "feels" heavier at a stand still and when picking it up off the ground due to perimeter frame fuel tank placement up high, but on the trail, the gyroscopic effect of the weight of the small bore engine internals being lighter on the 200/220 and the short wheelbase really make our "antiquated" KDX's shine on the trail. I really surprise all the 30-50 year old casual riders in my group, at 160lbs & 46 years old myself (granted most people think I look like I'm early 30's), with how much they struggle to keep up with my pace on my "old school" KDX... and they're generally all on modern 300's, a 500 4 stroke, a KTM 250 SX etc.... I'm not much faster on the fastest bike of the bunch a '99 CR250R Honda MX missile, but if the suspension were set up for woods, I'd probably be untouchable on that insane bike - just not on the technical slow trails lol, it has an insane ignition curve that goes from creeping along immediately to spinning the rear tire.

Something in between the Beta XTrainer 300 and the YZ250X is really the equivalent of a modern day KDX200, and the Reiju MR Ranger 200/300 as well.


Are you talking about the common WR250 4-stroke transmission? Or are you referring to the mid 1990's 3-year or so model run of the WR250 2-stroke? Not to mention the rare early/mid 1990's WR500 2-stroke, one of the two greatest air cooled enduro bikes ever (the other being the '86-'88 KDX200!).


I fully agree on the YZ250X being an amazing bike. Aside from the lack of a 6 speed gearbox, they really could use a tighter squish band head configuration same as a KDX220 suffers from stock, but swapping to a YZ250 XC dome Apex Technical Innovations cylinder head fixes that on both the YZ250X and the YZ125X woods bikes. The 125X is a sweet machine and the lightest woods bike out there. The 2006+ YZ's also have the best suspension available on any woods bike, the KYB S.S.S, although the Showa Twin Chamber forks 1998/2001-2004/2005+ are nearly identical in design but just different factory tune spec.
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Re: YZ250X...the next KDX?

Post by Chuck78 »

The only issue with giving the YZ250X a title as lofty as "the modern day KDX" is that all the veteran riders look so highly upon the KDX's as they were the "Best Woods Bike of All Time" back in the late 1980's and 1990's when they had very little competition in the form of factory trail bikes (WR250 and RMX250), and were mostly up against motocross bikes or the XR250/XR400R... Nowadays, many of the 20-something and early 30's riders talk trash about the YZ, claiming slight stretches of the truth "cool a bike that hasn't been updated for 20 years, yeah that's a competitive machine (sarcasm)." They don't get the respect that older riders in the know will attach to the KDX platform...

All that aside, if Yamaha would just add a wide ratio 6 speed gearbox, e-start (two companies make this in the aftermarket now for YZ's), and a lighting coil from the factory, as well as a slightly larger 2.2 gallon fuel tank so that they had the same tiny capacity of the modern 300's, the YZ250X model woods bike platform would really really give the overpriced Austrian bikes a run for it.

One thing to note thouugh, the $14,000+ trail-ready trail-prepped price tag of the new KTM's finally came down for the 2024 model year, as it seems that WP Suspension / KTM finally got their head screwed on straight and came up with a legitimate suspension setup after 25 years of constantly being in the shadow of the Japanese suspension companies. The 2024 forks are the first really great fork KTM has had since KTM got popular in the 2000's, so one no longer needs to immediately spend $2000 at a professional suspension tuning shop to get their expensive machine to ride properly like a stock YZ250X or Beta RR Race Edition...
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Re: YZ250X...the next KDX?

Post by bufftester »

The WR250 tranny is the target. People know the KDX, but the WR and the RMX250 just were'nt around long enough to gain the following they deserved. My son is currently riding a 95 RMX250, and nobody in our riding group (most of them on XC-Ws and TEs) can keep up with him. It also has a 5 speed gearbox, but 5th is REALLY long on it. Everything I do in 2nd/3rd he can do in 2nd alone. And oddly enough it "feels" like a KDX when you ride it. I agree that the title is a lofty one given all the "hard Enduro" fan boys out there, but for the other 95% of riders I think it would be a good fit.
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Re: YZ250X...the next KDX?

Post by SS109 »

I know the X is a really good bike other than the shortcomings already mentioned. I rode my buddy's X on a 6.5 mile loop that I'm very familiar with and, even though it was set up for his weight and riding style, I was less than one minute off of my best time ever which was set on my old '90 KDX. The X is a fully capable bike and would be awesome if they would just upgrade it a bit.

The big thing I didn't like about the X is the wonky transmission gear spacing. Sorry but it just plain sucks. I have heard over on TT that a WR450 5sp trans, which has much better gear spacing, will drop in with just a slight amount of clearancing on one of the case halves. I tried to talk my buddy into doing that, along with one of the e-start setups, but he said he would rather just buy a new Rieju and get the 6sp, e-start, and hydraulic clutch from the factory.
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Re: YZ250X...the next KDX?

Post by bufftester »

Yeah, the tranny gearing is just not good. The Rieju is also a good alternative, but really is just suffering from brand recognition more than anything else. I know that Moonstomper has had a lot of good to say about the Rieju, I just have not had a chance to ride one yet.
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Re: YZ250X...the next KDX?

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bufftester wrote: 04:12 pm Mar 21 2024 The WR250 tranny is the target.
I'm not quite sure exactly what you meant by that? At first I thought you meant maybe the WR250 4-stroke or the rare WR250 2-stroke transmission is the goal to swap directly into a YZ250X to get a 6-speed or better gearing, but then I read something down a bit further about the WR450 5-speed gearbox being able to swap directly into the YZ250X with some minor case clearancing to clear a gear or two.

bufftester wrote: 04:12 pm Mar 21 2024 People know the KDX, but the WR and the RMX250 just were'nt around long enough to gain the following they deserved.
My son is currently riding a 95 RMX250, and nobody in our riding group (most of them on XC-Ws and TEs) can keep up with him.
I'm always riding a KDX220, & I resemble that statement, & I absolutely love that... There's only one guy that I regularly ride with who is faster than me, and all the rest of them on late model 300 2-strokes and 2 500 EXC-F 4-strokes as well as a KTM 250 SX & two 250 XC-W's generally all tell me it's all they can do to attempt to keep up with me on the mid speed flowing winding woods trails on my old KDX...
One 300 owner told me those very comments and said "dude you just absolutely float that thing (the KDX220) through the trail,..." At which point I'll say that this is why a smaller bore engine is better, because it's easier to make quick directional changes on the lean angle of the bike from extreme right lean to extreme left lean etc.
The larger heavier internals of especially the 300 balance shaft engines will give more of a gyroscopic effect, so even though the KDX feels heavier when standing still and rocking it back and forth, it's easier to toss around when in motion versus a bigger heavier engine.


bufftester wrote: 04:12 pm Mar 21 2024 I agree that the title is a lofty one given all the "Hard Enduro" fan boys out there, but for the other 95% of riders I think it would be a good fit.
Hey I resemble that remark a bit as well! I love the rugged nasty stuff, steep, rocky, rutted, challenging, technical... With a skilled pilot at the helm, the 200's do it well, 150's do it well...but really, the mini-300's do it best! By mini-300, I mean the KDX220R...
After having to ride all three bikes on the hardest obstacles on the hardest trails we've ever hit one year and one week ago, the KDX 200 with the ignition set for the higher RPM rev out / higher peak power ignition timing lower mark was a STRUGGLE to make it up the slow technical stuff although I got used to it on the first steep nasty hill after 2 stall-outs, but it was like riding a 125 motocross bike but just with a smoother Power band transition. The KTM 200 XC-W with the adjustable power valve in the generally most preferred "Langston" setting, unknown static timing setting at the stator plate, with the aggressive ignition curve setting (since the mild mode is basically nothing anyone would ever want to use unless it was really really slippery and not terribly difficult technical terrain), + one tooth larger rear sprocket, did pretty darn well - but not nearly as good as the KDX 220.

A YZ250X with the Apex Technical Innovations XC-dome cylinder head or a stock head milled down and machined to the same profile would do equally as good as the KDX 220, and comes with incredible suspension stock, the best on the market to be quite honest.

My buddy just switched to a 300 because he wanted better gearing or a six-speed transmission, and said that it was a step backwards for him in riding because he's struggling to do the hard enduro stuff that he easily did on the YZ250X, on this new 300 now... The YZ250X has a slightly shorter wheelbase and is definitely lighter... The cliche "Hard Enduro Fanboy" types don't have an open mind enough to give the smaller bikes a chance generally, and the 300 engines themselves do make the hardener out easier, but with the drawbacks of being a heavier engine, greater gyroscopic effect making it more difficult to toss the bike around quickly, and the longer wheelbase that those bikes have. So don't let someone tell you that you have to have a 300, because there are some young kids and even 70 year old guys alike that will smoke most of the 300 guys on their 150 2-strokes in woods races and even a few doing Hard Scramble type races and terrain on 150's...
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Re: YZ250X...the next KDX?

Post by Chuck78 »

I've been urging my CRF230 riding coworker, who just switched to bikes from riding quads at the age of 51 I believe, to go test ride someone's YZ125X as he's looking to buy something upgraded, and possibly a 2-stroke, but he thought our hot rodded KDX 220's were a bit too wild for his taste, so I've been suggesting he primarily look for a YZ125X or Beta 300 XTrainer. 125 vs 300 2-strokes are a huge leap in size, but the X trainer is quite mild, has electric start, lower seat height, light years better suspension than the CRF 230, etc... The YZ125X from what I've read surprisingly lugs decently, but definitely will require a little bit more clutch work. I haven't ridden one, but I'm sure it has more low end power than his CRF 230, that bike is anemic and with the worst suspension that I've ever ridden on any serious trails. He'll be so much faster on a bike that actually has good bump compliance on the trail trash... He won't struggle making it up the steeper hills when he hits a root or Rock that would otherwise kick out the CRF 230 front or back tires.

I think the Apex head with the XC dome for the YZ125X might be quite a surprise in terms of lugability and rideability, and is absolutely going to be the lightest bike on the market for a full size woods bike, as well as like I said having the best suspension on the market stock...
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Re: YZ250X...the next KDX?

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I think the yz250x will have a cult following later on when the newer tech bikes just keep getting more and more complicated and expensive. I’m sure it’s not widespread, but if you see the complaints on FB about the 23-24 ktm 2 strokes….people are ripping them left and right about them blowing up with their Kymco made cylinders and mapping that just isn’t there yet.

I think another bike that will be hoarded later is the 17-18 husqvarna TX 300. Counter balanced electric start and a carb. Of course with that is the 17 and up 250 and 300 ktm XC, pre TPI or TBI.
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Re: YZ250X...the next KDX?

Post by SS109 »

Chuck78 wrote: 10:12 pm Mar 22 2024...so I've been suggesting he primarily look for a YZ125X or Beta 300 XTrainer. 125 vs 300 2-strokes are a huge leap in size, but the X trainer is quite mild, has electric start, lower seat height, light years better suspension than the CRF 230, etc...
Another great option is the Rieju Ranger in either 200 or 300cc sizes. They come with decent suspension, 6sp, e-start, hydraulic clutch, lower seat height, mild tuning, can be made to Race edition power with some parts changes down the road, and the price is only beat by the YZ250X. IMO, it is the best starter bike option out there right now.
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Re: YZ250X...the next KDX?

Post by MoonStomper »

A lot to digest here! My buddy is back to racing his KTM 150 again. He tried the Beta 200, a KTM 250 4T and some KTM 200s before switching back to the 150s (bought a new one). Never considered the Riejus though. My son is still on his Rieju 300, he loves it and is bad fast on it. He says he wants a GasGas next. Honestly, I don’t like riding his bike. For me it’s too tall, too stiff, too long and too nasty. Perfect for him though, he’s a couple inches taller than me now and benches 350.

He’s gunning for a 250 A championship this season, so we’ll see how that goes. Oh to be nineteen again!
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Re: YZ250X...the next KDX?

Post by lucy »

Some very nice commentary in this thread by the participants.

I was looking long and hard for another KDX but decided I wanted something more modern and easier to find parts for. I bought a 250X with modified squish band but sold it and kept my 250FX because I thought I wanted compression braking. The 250X handles well, feels light, and stock jetting is spot on at sea level with the #40 power jet. Stock exhaust is better than aftermarket.

The 250X is an awesome bike. Nice smooth power with the squish fixed and the power valve mod with a little change in sprocket sizes. Small tank and kick only are old news.

Then went to a KTM 500. Decided I wanted something lightweight and was looking again for a KDX. I purchased a 2020 YZ125X and that thing is way dude fun.

At a little over 200 pounds you can't get much lighter than the 125X and KTM 150. Downside of 125X is small tank and kick start only. But, you look at the kickstarter and it almost starts itself...even with the Apex head. Stock jetting at sea level is almost spot on. Wheelies? Well, I haven't quite gotten the technique down yet and it won't roar like my 500 did.

I also have a 2019 carbed KTM 150 XCW that I haven't really manhandled yet. Its e-start and bigger tank. A few more horses than the 125X.

I'm working to sort out the small bores. Had my eye on Doug's national champion KDX since he is just up the street but one other lucky slob stole it from under me.

The 250X is where I would be if it had electric start. At almost 70 years of age I don't want to hassle with a kicker if it torques my knee.
Last edited by lucy on 04:49 pm Mar 25 2024, edited 1 time in total.
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Re: YZ250X...the next KDX?

Post by Chuck78 »

lucy wrote: 11:05 am Mar 24 2024 I bought a 250X with modified squish band.......The 250X handles well, feels light, and stock jetting is spot on. Stock exhaust is better than aftermarket.

The 250X is an awesome bike. Nice smooth power with the squish fixed and the power valve mod with a little change in sprocket sizes. Small tank and kick only are old news.

Decided I wanted something lightweight and was looking again for a KDX. I purchased a 2020 YZ125X and that thing is way dude fun.

At a little over 200 pounds you can't get much lighter than the 125X and KTM 150. Downside of 125X is small tank and kick start only. But, you look at the kickstarter and it almost starts itself...even with the Apex head. Stock jetting at sea level is almost spot on. Wheelies? Well, I haven't quite gotten the technique down yet and it won't roar like my 500 did.

The 250X is where I would be if it had electric start.

Nice, thanks for the commentary, lucy!

I've been really curious about the YZ125X myself, as I've only ridden YZ125 & CR125R motocrossers.
My main point of curiosity is how luggable the lower midrange power is when trying to creep up steeper technical hill sections, and if doing significantly technical work going up steep hills would be pretty tricky with them, or if this just requires keeping the revs up a little higher & gearing up a few teeth on the rear sprocket?

If I had a lot of disposable income, I believe I most certainly would want to buy one and add full Enduro gear to it - oversized tank, Apex Technical Innovations XC-dome cylinder head, Hyde Racing skid plate, pipe guard, and the 60W lighting coil kit and a headlight, hand guards, as well as most likely an all black plastics kit. I'd be really tempted on first rebuild to bore it out to 134cc. For some reason, the former owner of Apex cylinder heads (now Lead Fuel Systems Engineer at Lectron) advised me against taking a YZ125 out to 144cc, but I don't recall his reasoning as it was very brief, and I didn't pry for a deeper explanation, but being the YZ125/250 guru he is, I noted that ot should definitely be kept to 134cc for best overall performance. Perhaps with the YZ125X woods porting being drastically different from the YZ125 motocross porting, the X won't see as high of RPM and would do fine with a slightly heavier piston? It might have just entirely been due to the cylinder wall thickness especially the unsupported portions protruding beyond the base gasket into the crankcase would become too thin?

I always wondered why Yamaha didn't just make it a "150" @ 144cc like all the other small bore full size woods bikes... Probably just to keep the parts warehouse less inundated with parts that could have a wider interchange (1 125 piston for X & MX versions vs 2 different pistons).

Feel free to add commentary on that 144cc vs 125cc question.


I'm mostly curious how well the YZ125X lugs or creeps up steep technical hills...
My buddy's KDX 200 with ignition timing set for high RPM power vs low end torque, it rode like my brother's CR125R when tackling very steep slow hills, it just stalks out due to lack of low end torque... Until we advanced the 200's ignition midway between the middle and upper mark (from all the way at the lower mark), then it came alive!

I'd read the YZ125X did surprisingly well for a 125 in terms of lugability, but I'd like more feedback on that, especially as I'm pushing my coworker to shop for one. He's shorter @ 5'7"-ish and doesn't want a tall heavy bike but badly needs an upgrade over his abysmal CRF230 - very underwhelming low end and high end power on that thing as well as archaic suspension that's no good for anything bumpy off-road.
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