KX144 / KX134 / "KDX139R" big bore KX125 woods bike? Low/mid woods porting & high compression head, woods conversion???

[Chuck78]

So I'd been trying to convince my brother to do a 134cc or 144cc woods porting big bore conversion on his '00 CR125R MX bike. That along with the top heavy weight of our '95+ KDX's versus an "inferior" center spine frame (like the E series & KTM woods bikes which carries their gasoline weight lower, for a lower center of gravity and a lighter feel) got me dreaming of building a woods-ported '96+ KX134/KX144 in order to get the lightest possible full size woods machine...

96 KX125 purple

maxresdefault-2.jpg (307.57 KiB) Viewed 15629 times

I LOVE my purple KDX plastics and graphics, so if I did a KX144, it would obviously lean towards the years that are compatible with the purple 96 plastics and graphics, but SKDA out of Australia make purple checkered flag '96 KX styled graphics for all KX/KDX/KLX/KX-F models 1995+, so that opens it up to anything 1996+ KX125 2-strokes.

https://us.skda.com.au/96-factory-kx-full-graphics-kit/


The purple with checkered flag graphics really does it for me... But now I see I can get this style from TFB to fit '03+ KX125 shrouds, & SKDA offers variations on this to fit all '95+ KX/KDX/KLX/KX-F models, I'M SOLD!!!!

KX250-Radiator-Shroud-Graphics-PIC.jpg (208.67 KiB) Viewed 15629 times

Woods mods definitely will have the porting altered for low and mid-range torque at the expense of a mellowed out high-end, 6 oz or 8 oz flywheel weight added, or even 12oz, the head reworked for maximum compression allowable (requiring race gas) as this adds substantial low end torque, as well as widening the squish band profile of the head and tightening up the squish band height clearance, and possibly a Lectron Billetron Pro Series or Smart Carb SC2 35 if they have come out with the KDX 35mm version by then, or possibly SC2 36 (all metering rod style carbs).
A KX134 or KX144 seems like a better investment of time if you're concerned with ending up with a SIGNIFICANTLY LIGHTER bike than a steel framed KX-KDX hybrid...

The potential of having a bike that was considerably lighter than my KDX, or a lighter than a heavier KDX engine in a 125 chassis at great labor time expense to only save 6lbs overall building a hybrid over the course of months, you can just run upgraded suspension and less gasoline weight in a KDX and achieve the same performance in my opinion...




I've ridden a pre-KTM (Ducati owned them until 2014???) Husqvarna CR144, was an absolute animal in terms of power and throttle response... It didn't feel any different than a KTM 200 that was tuned to the maximum power output.

I have read a lot of accounts of people doing the YZ 144 conversions and absolutely loving them for woods or MX, no matter which of the 3 porting options they got to cater towards their riding terrain / riding style - high end power, more power throughout the entire rev range, or low/mid range torque porting which is basically the "more power everywhere" porting but with the cylinder base machined to have the cylinder sit lower, and the head's combustion chamber quench areas machined accordingly.
I've read similar accounts for the RM144 and KX144 conversions, owners saying that the bike is super fun to ride and actually HAS low end power / torque now. Only one post on this forum said that the low mid porting 2000's KX144 set up for desert was still a bit of a handful in the tight slippery Pacific Northwest woods riding.


I'm really curious about people's experiences with the Eric Gorr (& others') low/midrange torque porting on a modified head, with flywheel weight & 144cc's, & possible smaller carb swap... Having two KDX220's, I much prefer the 220's power delivery over her KTM 200, but her KTM is definitely lighter, and having chain glides on the swing arm instead of clunky rollers, definitely makes the bike feel smoother as well, something that always bothered me about the clunky KDX lower chain roller. I'm just wondering if a 144cc built for torque with a flywheel weight would be satisfying enough and capable enough on the tight singletracks.
I know a lot of people run the YZ144 with the similar porting from Eric Gorr, and absolutely love it on the woods riding & singletracks, many preferring it significantly more than their 300 two strokes due to the weight and fun factor. But everything is relative, plenty enough low end grunt according to one person might be extremely disappointing to another, & people's available riding area terrains vary widely.

[Chuck78]

I've gone deep down the rabbit hole the past few days reading about 125 MX'er big bore 144cc woods conversions via Eric Gorr/Forward Motion's engine work, after initially just looking into this trying to get my brother riding with us again on his '00 CR125R after a long hiatus...
Gorr's #2 "more power everywhere" porting option 144cc treatment with pump gas head mods would really help him out tremendously when riding anything other than wide open areas, as he never hits motocross tracks ever but just likes the explosive power hit and very easy handling of the lightweight 125.
However, anytime we went off on some tighter singletracks or off-trail bushwacking, he always had CONSIDERABLE difficulty even with the heaviest flyweight and the largest rear sprocket he could find for that 125 (he did say that both of those helped him substantially, but still not enough).
I feel that a KTM 200 EXC or XC-W would be the perfect bike for his tastes, but he's not in the market to buy another bike currently.

These days, we ride even gnarlier more rugged terrain than 6 years ago when he last rode with us...
After riding yesterday, Nov. 26th in Ohio (cool wet weather season) on some wet, slick, leaf covered North facing slopes in Wayne National Forest on singletracks and getting stuck on some steep hills, muscling/lugging & jockeying around my KDX220R on two steep hill spots where it was too slick to make it up 15-inch+ steps with roots and wet clay / leaves, and picking up my wife's KTM 200 many many times (still a lighter bike than the KDX by 14-15lbs, lower center of gravity especially), the thought of having a bike even lighter than her KTM that was "capable enough" (luggable low-mid power) for this kind of riding, seemed VERY APPEALING...

The only major flaw of the KDX platform (figuring in the easy ability to upgrade suspension etc) in my opinion is that it's top heavy. Most of that is due to the gasoline weight being higher up due to having a superior perimeter frame (as well as having a larger tank which carries more gas higher up then the KX gas cap sits, and how this perimeter frame mandates more gasoline weight be carried up slightly higher rather than lower. A lot of modern bikes have aluminum detachable rear seat subframes, but that's really not going to save you significant weight, only a slight bit. Swapping out KDX forks and shock are significantly easier than cutting and welding and grinding to fit a KDX engine into a frame which it doesn't fit and custom making an exhaust to accommodate both.... For this reason I've never thought that it was worth it for me to build a hybrid with the amount of custom fabrication work involved versus just upgrading the KDX. You're putting a 12lbs-14lbs heavier engine into the formerly lighter bike, adding skid plate, hand guards, oversized gas tank, lighting coil, headlight, light switch, rectifier, tool bag, etc so the lighter bike is no longer SIGNIFICANTLY lighter than the KDX, but they are a bit more slender in the knee areas still and you will end up saving about 10lbs over a similarly equipped KDX.

[Chuck78]

No opinions on this??!?!?!

I've read a lot of of accounts of people doing this conversion with the more power everywhere porting and a few with the low end porting, but would really like a good frame of reference comparing it to the luggability of a KDX 200 or 220 engine....
I suppose that Eric Gorr could definitely do porting that will significantly enhance the low end of a bike that has a non-existent low end, and I'm sure that adding a 6 oz or 8 oz flywheel weight would definitely help, I'm not sure about a 12 oz as that may take away too much from the upper mid-range for when you really need more power.

Most manufacturers stopped making 200 cc bikes throughout the years, KTM was one of the last holdouts and finally canceled their 200 in 2016 in favor of the more perfected versions of the 2007+ 150 XC/XC-W as it's replacement in the lineup. Yamaha pulled the plug on the IT200 way back in 1986, & Suzuki never even got to the point of increasing their 1980-1984 PE175 2nd gen engine in the new 1982-1984 new Full Floater monoshock 3rd gen PE chassis up to a 200cc to match the IT200 & KDX200, as motocross was hugely popular then vs woods racing, and most enduro racers were on motocross bikes perhaps as a result or due to their more aggressive power

Reviewers of those 144cc "150" bikes say they are a ton of fun but obviously due to the smaller engine you have to use the clutch and throttle a lot more.

Heck, people make pretty sweet woods bikes out of the smaller 16"/19" adolescent-sized Kawasaki KX100's just by gearing them down and adding a heavy flywheel weight. There's no doubt this will be a doable feat, although it certainly would require more clutching skills and a more experienced rider on the technical stuff. I'm just trying to get a good idea of what to better expect if I were to put some $$$$ into this.

The 1996-1997 KX125 was originally my top candidate due to the classic stylings & availability of purple '96 plastics & graphics. This is just a pipe dream at present as I have two vintage Suzuki's and my '99 220 all awaiting major rebuilds and restorations. I may sell a 1983 Suzuki PE175 Full Floater soon though, and a Suzuki GS1000 or GS750 street bike, to fund a '96-'08 KX125 or possibly an '86-'88 KDX200 (I'd sell my '77 Suzuki PE250 as well if I got an '86-'88 KDX200!).

1999 KX125 was a similar chassis but a different aluminum seat subframe, in aluminum now, and different stylings. '99 was a 1-yr-only piston, although not a whole lot different from the others.

2000 was my newer top candidate. This year had a heavier flywheel and more low mid-range torque oriented porting, or at least an emphasis on mid-range torque, as most 125MX bikes don't really have much in the way of low end torque at all. '01-'02 were largely the same aside from porting for more mid-range and upper rpm, and a lightened flywheel. Forks changed a bit throughout these years internally.

[Chuck78]

I may just have to call Eric Gorr and ask him myself what to expect of the low/mid torque capabilities in technical 1st & 2nd gear steep rocky rooty terrain.

Having a bike that's significantly lighter than the 1995+ KDX would be really fun. I've ridden my brother's CR125 a bit, and wow is it significantly easier to whip around. The aluminum frame, Motocross suspension, and stock screaming high RPM monster of an engine with zero bottom end all presented different challenges though... No aluminum frames here, unless it were a YZ250X or YZ125X woods bike...
(Why on earth did Yamaha introduce the YZ125X woods model a few years ago and not make it a factory 144cc big bore version to begin with, when most other manufacturers all have their comparable bikes as a factory 144cc aka "150?")

[KDXGarage]

Does Beta still make a 200cc?

[MoonStomper]

Chuck,
So after chewing on all this and reflecting… based on my recent experience riding my 17 year old son’s recent bikes - ‘08 KTM 144 SX - modded out for woods racing, his ‘08 KTM 200 XC-W, his current ‘22 Rieju MR300 Racing, and my own hare scramble race-tuned ’03 KDX 200…

My KDX compares to those other bikes …
… the 144SX lacked the low end power but handles like a mountain bike, for fun-to-ride-smile-your-face-off factor it was hard to beat, you just wail on the clutch like Eli Tomac and you go places. Maybe not the bike I choose on steep terrain days. My buddy has the newer KTM 150XC, he previously owned my son’s 200, raced it, decided he preferred the 150, so he bought two. He’s a 50A rider, and won his recent B class championship on one.

… the 200 XC-W just about had the power of my KDX, but handles easier and is lighter. Doesn’t quite tractor like the KDX, it had more of everything than the 144 and was easier to race, especially on the steeper terrain. I like it’s lower CG, don’t like the problematic, leaky, hydraulic clutch - same issue holds on that 144 too. My son prefers this bike to the 144 because he says it’s easier to race. He races at a high level and is super intense. He hated that he would get beat in the straights by kids on 4 strokes after whipping them in the woods. He did get a lot of hole shots on the 200 though.

… the new MR300 Racing is quite the beast. Handles everything you throw at it, super easy to race, just click 3rd and hang on. Easy to get parts, dealer and brand rep support has been top-notch. E-start makes it super friendly in the bad places, has a lower CG than the KDX, and insane KYB suspension that lets you feel like a pro everywhere. If I wanted to do a hill climb competition this is what I’d take it is quite the tractor. If I could afford one, I’d be very tempted. My son says the 4 strokes don’t give him trouble anymore.

After riding all these quite a bit in hard western Virginia mountain terrain over the past three years I do have soft spot for that 144 for all the reasons you like that size bike. I think what you are planning sounds like fun, I’d like to try this purple KX144 when you finish it. I hope you go the “power everywhere” route. Seriously, that 150 size is Goldilocks.

A few weeks ago my buddy and I swapped bikes for a couple laps at one of our closer hare scramble venues (Rattlesnake @ Wythe Speedway). I was immediately faster on his bike in all the tight, nasty stuff, but missed my KDX’s low and top end power. Probably the 150 would translate to faster lap times and more podiums for me. Your idea sounds really tempting and a lot of fun for a lot less money. If I get serious about racing this is an interesting idea, I think you could build something sneaky fast.

[SS109]

Personally, I think the small bore bikes (under 200cc) are a good choice for very aggressive and experienced racers. However, they require excellent clutch skills to get the most out of them.

@KDXGarage Yes, Beta and Rieju both make 200's. The Rieju Ranger would be my choice out of the two. It's more like a modernized KDX with kick and e-start, 46mm KYB forks and KYB shock, turns better than the Beta (the Beta can't turn really tight), has a low seat height compared to their MR race bikes, and can be hopped up easier.

[MoonStomper]

RE: Rieju Ranger 200…
The only thing our friend did to his son’s bike was upgrade the pipe for racing. The bike is lower than the Racing version, but mostly identical otherwise. Super nice parts on these bikes and fast.

[Chuck78]

I was planning to get the low/mid porting as that's more suitable towards the terrain I seek out to ride, and also perhaps more beginner friendly if I wanted to have a bike to loan friends to learn how to trail ride with us.

I have a buddy that's been begging me to find him a KX100 because he's afraid of his DRZ400E and WR400R (both bikes that he took in on trade, he's a car mechanic) he says they're too big and heavy and powerful.... I wasn't quite sure a KX100 or the new KX112 would be the answer though but definitely easier to handle, definitely challenging on the clutching skills though. I myself also have been really lusting after a KX100 adult woods bike play bike conversion... LoL although the adolescent-sized 16" rear 19" front wheel combo will make it a lot more challenging on the nasty stuff we ride so it would be limited to more mild off-road scenarios I suppose... This is where a low midporting KX144 might really do it for me, and the frame and ergonomics would be the appropriate size for me at 5'10" and 155 lbs (vs a KX100/KX110)



My whole purple 96 KX144 idea came after pondering a CR144 mod for my brother to get him to be more capable of riding woods with us on his '00 CR125R, and also more for my desires as the KDX is fairly top heavy and it does get tiring picking it up when you get stuck in the middle of a steep rutted hill or drop it in the rocks on a steep hill.
But wow even with stock KLX300R forks redone, and a rebuilt shock, + Neutech TUbliss with great tires and low psi, my 220 is just a dream in the woods for nearly everything aside from picking it up in precarious steep nasty terrain situations..., & Finding the limitations of the open chamber forks when racing hair scrambles and riding twice as aggressively as I normally ride. The KDX220R (& probably a KDX200E with suspension mods) is definitely better in the nasty woods than a KTM 200 XC-W or KDX200H... But all of these bikes are simply awesome, don't misinterpret my statement. I do feel a bit awkward learning to jump big logs (downed tree trunks) with the top heavy nature of the H-series perimeter frame fuel tank placement perhaps contributing to that, but my skills in this department are lacking seriously in coordination lol...people hop logs on 400/450 4-strokes all the time and they're far more top heavy.

[Chuck78]

As far as the Rieju bikes go, although they aren't the most popular and parts are less commonly available, I have never heard a single bad thing about them and only immense praise by those that have ridden them.
That's good to know it turns better than the Beta in tight off-road scenarios. Now if they only made something similar to the Beta XTrainer 300! I've been thinking about trying to push my wife to get one of those, as she really needs electric start in a lightweight package with a low seat height and top shelf components, otherwise her '07 KTM 200 XC-W does quite well and is a bit lighter than the KDX and absolutely has a lower center of gravity with the center spine type frame and the fuel weight hanging down low on the outsides instead of all up high in the perimeter type frame like the KDX has, although the 200 XC-W just wants to aggressively accelerate even with the mildest power valve setting and heaviest flywheel weight, it just takes off like an ANIMAL. I need to look into further alterations of the ignition timing perhaps...
The biggest issue is that it's just very tough for her to kickstart after the bike has been dropped in the nasty gnarly terrain (which happens very frequently), it seems like it always floods out slightly and although I can get it kick started in these scenarios in one or two hard fast kicks usually, it takes the extra oomph that someone that's 5'3" with short legs does not have....
Her KTM 200 XC-W is a 2007, which was the last year of the lower seat height models for KTM unfortunately, and predates any electric start conversions by several years.
We further lowered the suspension internally and shaved the seat foam down so that she could touch the ground. She has short legs and is 5'3"... She's quite attached to this bike because of having it lowered and seat shaved and knowing that 200s are top-notch high quality competitive bikes...

...but on the twice a year women's dirt bike camp out at Wayne National Forest, this Fall ride was the first time that she was the only one that had a kick only bike, all the other women had electric start bikes.... The spring ride they do that's more beginner friendly as well as having advanced groups, there are a few with Kickstart, but all of the serious ladies all have a start bikes except my wife. And she's the shortest one of all and has the most trouble kicking a bike to life... Tough sell, she's very set in her ways and stubborn, can't convince her so well that and he start bike is what she needs although she knows it inside lol

With as low as her KTM is, one of these 150s be it a big bore 125 or the KTM 150 XCW, would not be significantly lighter, maybe 10 lbs, but the east start on the newer model certainly would be nice.
The Beta XTrainer 300 2019+ advertises a 219 lb weight which is pretty phenomenal, that's really not much heavier at all than her KTM 200 which is advertised at 221 but I feel it's lighter than that, whereas the KDX advertise at 223 realistically is more like 233 with FMF exhaust even.

[Chuck78]

Update.... On the Beta/Rieju topic.
A quick glance at the Rieju website shows me the Rieju MR Ranger comes in both 200cc and 300cc versions.... And the seat height lists "903 mm +7 / -31mm"

907mm-31mm is around 34.3"... And the suspension is said to be softer than the other "Hard Off Road" models... I assume hard off-road means hard enduro/agressive trail riding. The "Off-Road" bikes look to be more casual woods bikes.

So to me it looks like the MR Ranger 300 is probably a directly comparable model to the Beta 300 XTrainer... That's certainly got my attention.

I feel that Beta, Sherco, and Rieju ALL have KTM beat in the suspension department by far, even my buddy that has a 2017 300 XCW and brand new 500 XC (XCW? XCF?) tells me that KTM STILL hasn't gotten the suspension right on stock models...

Reading up on these 49 mm 96-98 Suzuki RM Showa twin chamber conventional forks, I also read a lot of references to the 1998 or so KTM conventional forks, and noted that immediately upon KTM switching from marsachi to WP inverted forks, no one was ever happy with the stock suspension when seeking out a plush woods ride for nasty terrain... I thought it was just the first generation or two of their suspensions, but riding my wife's 07, her forks are very harsh compared to my KLX forks when blasting through the nasty rocky stuff at second gear top speeds and into third a good bit, and other friends that have 2010s KTMs and even the guy that has the 2017 in 2023 complains the same, front wheel deflects off trail trash... People apparently have a lot of trouble tuning that out of these WP forks from what I've read all over the place.

So those other three European browns really have got KTM beat in the suspension department as it seems KTM is just destined to make harsh riding bikes for Austrian giants that are all over 6'3"!

Also, the YZ250X certainly seems like an awesome bike but people really are let down by the fact that it does not have an electric start option aside from the aftermarket $1,500 add-on kit, and they also don't have lighting provisions or have a really weak lighting coil, and the aftermarket kits aren't even as powerful as a Ricky stator for a KDX.

If it weren't for those two things, I would certainly rank it up there with the other 3 - Beta, Sherco, & Rieju... For all intents and purposes if you don't care about electric start and want to save money, the YZ250X is an awesome bike, ADV Monster sells a 38 watt LED headlight that puts out something ridiculous like 7,000 lumens... I'm actually going to try and get three of my KDX buddies set up with that, maybe my wife's spike also.

The suspension on the YZ250X is as good as it gets. One of our Pittsburgh buddies has one. AWESOME engine with a very long parts interchange from 99 or 2001 I believe.



Dimensions
Lenght x width x height : 2145 x 810 X 1215 mm
Wheelbase
1.475 mm
Fuel
9,8 L
Dry weight
105 kg
Seatheight
903 mm +7 / -31mm

[Tyl3r]

Was skimming through this novel and think you make some good points. I always wanted to try a <200cc two stroke, but have always heard they are best for the fast guys wanting to ride aggressively. Need to have good clutch control and always use momentum. While that is fun and I do like that sometimes, most of the time, I want to have some "tractor" ability on tap for the tricky stuff where I like to play, so I never went for it. The Beta and Reiju's do definitely look cool and sound good from what the magazines say, but I just worry about getting parts, they aren't as common (TM's included).

If talking about new bikes and you are going to have suspension set-up personally anyways, curious why you discount the 300 XC-W? I'm no racer, but when I go to enduro/woods rides where there's a lot of people, the majority of bikes are KTM family 300's. After trying some out, I can see why... and I am also strongly considering a 2024 300 XC-W to be honest. Like you said, 3rd gear and hold on it. Haven't been on one with suspension I hated yet. I dunno, they are pretty sweet if you ask me. If you break something while out on one of those rides, chances are, someone might have a spare to help ya because they are so common. If its just wanting to not have what everyone else has, I get that...that's why I ride a hybrid lol but to me, there is some pretty sweet tech out there. I'll always love my hybrid and don't see me ever really selling it, but I still want to keep up with the times (but I'm still not getting a tik-tok).

Also wanted to say about frames on the 125's. The 03-05 125's have the wishbone frames and they don't have a top heavy feeling like the KDX. Riding a hybrid then a normal H series back to back is a huge difference. The two bikes weight different by like 5 lbs (if that, maybe) but the one with the KX frame felt worlds lighter and much easier to throw around in the woods. I think that generation KX is still a fun one for sure, would be even better with the sweet Showa suspension swap!

You know what, after thinking about it a little, to have the perfect bike...I think you just need to go all out and build a hybrid

[Chuck78]

@Tyl3r you make some critical points about the hybrids... I didn't really look into which if any KX frames strayed away from the perimeter frame and back to the center spine wishbone construction...but yes, similar weight bikes can feel drastically different in weight due to where the fuel weight is carried... So perhaps a perimeter frame'd 192lb or 196lb 94-98 KX144 may feel a lot lighter than a 95-06 perimeter frame'd KDX, but from what you're pointing out, an 03-05 KX125 frame whixh apparently went back to a wishbone design, will "feel" far lighter than a similar weight 94-98/99-02 KX125 perimeter frame model... Hmmm.... If I were to follow through with this brainstormed project, I really wanted a purple '96 KX125 tho!!!

This is however motivation to do a 98 RM125... It has a center spine frame with the gas tank hanging down on the sides lower...
No aftermarket tanks available, but I've read that Suzuki tanks are very cross compatible with little or no mods - an RM250 96-00 tank directly swaps to the 96-00 125, and 1998-ish RMX250 tank probably would as well.

[Chuck78]

One other cool thing if I ended up doing an RM144 vs a 94-98 KX144 in 96 purple plastics/graphics - I wanted to get the 1998-ish RMX250 radiator shroud graphics like the 96 RM & KDX lettering/font, all black plastics (Clarke or IMS 3.0 or 3.4 gallon black 96-00 RM250 tank), & run the RM125 144cc big bore as an "RMX 150" by using the RMX shroud graphics and the RM 125 / RM 250 swingarm decals cut and spliced to make a 150 in the retro 1990's font, so that it'd be an all black plastics RM125 "RMX144" model... I was pretty excited at the thought, and they came STOCK with the Showa suspension that I'd want...98 49mm Showa Twin Chamber conventional forks being the absolute #1 pick.

Here's the later RMX250 for reference, with the same lettering/graphics style as the 96-97 RM125/250:

RMX250.jpg (269.15 KiB) Viewed 15476 times

RMX.jpg (230.66 KiB) Viewed 15478 times

Picture the similar appearing but smaller framed and all black plastics are in 125 with a shroud graphics and the swingarm decals spliced to make the same style but "150"... RMX150...cool



I'd also look into whether or not that shrouds or shrouds and tank from those years would swap onto a 2001-2008 are in 125 to be able to utilize the same graphics... Those have theu h more common inverted 47mm Showa Twin Chambers and already come stock with the shock that I would swap on to the older 96-98 RM125 which I also have two of here, to swap onto both of my KDX220's just like SS109 and a few others have done. They are an inch longer which translates to significantly more ride height, some internal lowering, backing off preload for more sag, and perhaps longer linkage dog bones to lower slightly, are in order to run this though on the KDX frame.
That would be truly an awesome combo as well...
My buddy and I were talking about this show is suspension last night at the bar, he was actually about to text our old co-worker to see if he could trade his CR250 back for the '98 RM250 that he sold our co-worker ages lol... The CRs always are known to have the more aggressive engines that era and earlier, but the RM suspension is always known to be the best all around up until the KYB SSS on the YZ models in 2005+ being equals with the Showa Twin Chambers...

And yes Tyl3r, not only do I get great satisfaction out of tinkering with my hobby machines and modifying them, but I do also like to be a little bit different than the overwhelming sea of orange bikes built for Austrian giants...

[Chuck78]

So I just watched some videos last night of the local nasty gnarly singletracks at Perry State Forest here in Appalachian Eastern Ohio, guys riding up a slick-as-snot mud covered bedrock canyon/ravine "waterfall" - and after many riders on 300's struggling and slipping around, and turning around before getting even halfway up this 200ft run, the very first rider of the day in this huge pack to make it UP the waterfall/bedrock ravine with slick wet clay mud coating everything - WAS ON A 125 2T MX'er! One of the cleanest passes of the few that made it up this gnarly nasty slick rocky run. The "waterfall" portion of the ascent, which was steeply sloped the entire way by the way, was about 7 feet tall and VERY STEEP, not quite vertical but very intimidating...

So that just proved to me that a 144 big bore conversion with the "low-mid" or "more power everywhere" porting + 91 octane pump gas head mods could definitely be a blast and still make it through this kind of stuff, but as I witnessed in the video, the small bore "woods bike" absolutely required the rider to be quite aggressive (he was on a 125 though, not converted to a 144 big bore)...
I think with a very plush woods revalve on the suspension, and appropriate springs, that a 125 big bore 144cc woods bike with these porting and head mods would really shine when ridden aggressively, as the plush suspension revalve with softer springs (.38kg for me at 155lbs, or even .36kg since the bike is 30lbs lighter than a KDX and I'd be running Showa Twin Chamber forks perhaps - which have a pressure spring that adds to the spring rate slightly like the nitrogen charge in our shocks basically), that one could keep the revs up and ride one of these machines more aggressively as the engine would require, but still blast up and over the more substantial trail obstacles without bouncing off of them substantially...
Too much bucking and getting launched airborne scrubs/robs all of your uphill momentum in the nasty gnarly steep terrain... so for my desires, I think this would be very critical. Cannon-Racecraft make lighter springs in .36 and .38 for the 98 R125/250 forks which I have a few pairs of, and .36kg may actually be warranted on the 125/144 due to it's significantly lighter weight. .38kg on KYB inverted open chambers on my much heavier 220 are PERFECT, I can use the whole travel range but it's not diving so hard so fast like the stock KDX .35kg springs. Drop over 30lbs in bike weight, and the .36kg coils may even be in order... Although it's better to have one size stiffer springs + softer valving, than to have firmer valving and softer spring rate...
*EDIT - I checked RaceTech's spring rate calculator for both a 96 KX125 and a 98 R125, and both state for 30-44yr old 154lbs singletrack rider preferring soft suspension, to run .37kg fork springs... so right in between the two available sizes, so either should work well with the proper valving... .38kg will be the first try.
UPDATE - I plugged the exact same info in but using the KDX220R as the bike, and it still gave me the same .37kg fork spring recommendation!!! The "223lbs" (advertised) KDX H-series actually weighs closer to 230lbs no fuel, WITH lighter FMF Gnarly pipe and FMF TC2 silencer... vs a realistic weight of 200lbs (193-196lbs advertised) on the 125's with 6oz flywheel weight perhaps, and add lighting coil / regulator-rectifier / headlight.
So I'm going to take that as a good reasoning to defer back to my thinking that for myself who ranges between 153lbs-157lbs, the .36kg may better suit my technical woods riding in this lighter chassis.


Now if I could just decide over a purple 1996 "KX144" versus a 98 or 05 RM125... anything RM125 for 96-98 or 01-08 would be suitable, but I'd only run the later 01+ with the intent of running the 1998-ish shrouds and graphics, and of course all black plastics... The Showa suspension on the RM's stock, and the frame/gas tank style of the RM125 contributing to a lower CoG / lighter feel are the primary reasons that the RM125 is in contention heavily. And I can mod them to swap around tanks and shrouds to be able to use the 96-97 R125 shroud graphics or possibly RMX shrouds/graphics to make it a blacked out "RMX 150" - which I was pretty fond of the idea of doing this never-manufactured fictitious model.

[Chuck78]

This potential build of mine is still quite a ways off in the future, but the curiosity and want are definitely there!

Browsing YouTube for fork valving vids I ran across for Doe Mtn Recreation Area (Tennessee) single tracks - a place that's been on my list of riding spots to check out.

Guy on a Husqvarna doing some slow steep rutted singletrack trail, I was thinking it must be a 300 with how low he's lugging it... Then I had a flashback a minute prior when Husqvarna TE150i flashed on the screen... Granted it's a TPI fuel injected model etc, but with how grunty that thing was and how effortless it seemed to ride, I'm sure an Eric Gorr 144 "more power everywhere" or "low-mid" porting build with a Lectron or SmartCarb, VForce or Boyesen Reeds, & woods valved suspension would be more than capable in the realms that I'm interested in... I do enjoy the fast flowy stuff as well, just to clarify!

Grunty lugger of a 150:



Nice... Brown Mtn OHV trails in Pisgah National Forest NC, possibly my favorite trails I've ever ridden...

I realized at the end when I saw in the description "2022 TE150i" that this was probably the same guy as above, more rocky slow technical riding, & the 150i just grunts right along! Granted an "old school" carb'd but heavily modded 125>144 conversion may fall just behind this in terms of lugability, I'd guarantee it could do the same stuff no prob with just a bit more clutch/throttle finesse...

[Tyl3r]

I only watched some of the first video and I must say, I am pretty surprised how much he is able to lug that 150, I didn't think it would be able to do that at all. Kinda makes you wonder...

[Chuck78]

I only watched some of the first video and I must say, I am pretty surprised how much he is able to lug that 150, I didn't think it would be able to do that at all. Kinda makes you wonder...

I was quite surprised also at how well that fuel injected TE150i was able to lug. Way more than I'd expect a 144cc to do so.
The 1st vid is Doe Mountain in Eastern Tennessee, that place is filled with slow goat trail singletracks.
The2nd vid are the Brown Mtn (Pisgah National Forest) North Carolina trails, they're just FILLED with rocks everywhere, like he quotes, it's "Like Moab with Trees" - but they are mostly pretty darn smooth flowing rock outcrops versus the rest of the Eastern US with sharp edged jagged sandstone primarily...

Well that certainly got me thinking that with a Lectron (or SmartCarb etc) on an Eric Gorr 144 kit with the low/mid porting, I should be able to get a KX144 or RM144 to run those trails like that, but I'd most likely run 'em a bit faster on the lower risk/less close trees sections... but I do definitely need the ability to lug when stuck in a steep tight spot - so the low/mid porting is still a big consideration, although *IF* I could get enough low end on the "more power everywhere" porting option, that certainly would make it more fun on the faster stretches. I do tend to ride more aggressively than most of those in my current riding crew (they ride pretty slow...I'm no Vet A racer but I do pretty darn well 8 yrs into woods bike riding after decades of BMX jumping/trails, MTB trail riding, and street bike corner carving)

I wish I knew someone who had a 94-98 KX125 for me to throw a leg over with a full tank of gas and see how the balance of the perimeter frame chassis feels, or even take it for a rip... or pick it up from a "staged drop." The purple 96 KX125 graphics would definitely be my top pick, but I'm still pretty into the idea of a 98 RM125 or 2001-2008 RM125, 2005 being the most desirable stock suspension year (closest to woods valving, 03 or 04 next, but 05-08 had a bigger shock shaft to be able to pass more fluid through the shaft more rapidly on big fast hits). The Showa suspension on the R125's is the top pick for me, and they have a center spine frame and clearly a lower center of gravity gas tank configuration due to the frame style.

[Kawiman]

I have a 2004 “KDX150R” that has the Eric Gorr low end porting and a high comp (race gas) head for better low end torque. It is really fun to ride, gobs more bottom end. I’m also using a 36mm Keihin air Stryker carb and a heavier flywheel (5oz iirc). Watching videos like the one you posted inspired me to build it. If you’re interested, I strongly encourage you to do it! Eric Gorr is reducing his shop and after 2023 will no longer be doing his port work! Act fast.

[Chuck78]

Thanks for the Eric Gorr info, I'll be looking to sell my '83 Suzuki PE175 now to shop for a '96 KX125...