KDXRIDER.NET

Although I've learned of shops that do 125 big bore stroker engines to the tune of 151cc and 167cc KX125's (with a 100 octane fuel requirement... and a hefty price tag at least for the complete engine build from the shop named MaxRpm), I've decided from riding a few 125's and many KDX200's & 2 KTM 200's, that I just really REALLY love a modded 220 engine above all of them... So I'm looking at a 99-02 hybrid build potentially, but definitely decking out 1 of my two 220's with an expensive dose of titanium parts all over, including the heaviest fasteners (axles, swingarm pivot, rear suspension linkage bolts) and a lot of smaller fasteners in order to really see how much lighter I can make it feel at least to pick up when dropped, or for very low speed gnarly terrain navigating...

Weigh that seat before buying Ti bolts. :-)

KDXGarage wrote: 08:53 pm Oct 23 2023 Weigh that seat before buying Ti bolts. :-)

You know I went down to the basement yesterday morning and grabbed my spare KDX seat, and it didn't really feel all that heavy to me whatsoever. Next time we have the seat off of my wife's KTM 200 that has shaved thinner foam, I'll compare the two, that's as close as I can get to a KX 125 comparison.

I'm sure the KX seat is lighter, but it didn't seem like there was all that much weight savings to be had there especially with the trade off for comfort.

That in combination with the aluminum seat subframe might make enough of a difference, as well as the fuel tanks being smaller on the KX models. Maybe the perimeter frame design slopes down a little further or is made out of lighter weight chromoly tubing on a KX? Hard to say.

I do have a spare 220 engine though, & an assortment of KDX H series pipes...

I'm still entertaining this idea for the long term, and spoke with Tom Morgan of Tom Morgan Racing, ex-Kawasaki factory race team mechanic/engineer and prolific KX500 engine builder and all-around Kawasaki guru. He said he regularly does 144cc KX125's, and has some good tested proven woods porting configurations for them... I'm leaning now towards keeping an eye out for a 2000-2001 KX125 & eventually doing custom purple '96 retro graphics , due to greater parts availability and piston interchange with the last generation of KX125 2003-2008, as well as better porting for low mid torque from the factory...
I still have yet to rebuild my other 220, or my two vintage woods bikes '77 & '83 Suzuki PE 250 & 175, but will be looking to move the PE175 to free up cash and space for either a '96-'02 KX125 or else an '86-'88 air cooled KDX200!

No matter which way you end up going, good luck with it!

I'm doing some work to my 1983 PE 175 2 stroke enduro to potentially sell it to one of two friends or anyone attending AMA vintage motorcycle days here in a few weeks. I'll be looking for a 1996-2005 KX125, please pray for me that my wife doesn't murder me for bringing home another bike!



I was discussing these 144cc woods bike options elsewhere pretty heavily recently. I've also read some reviews of various model years. It seems that the 1998 engine revision was unimpressive in the power output, & perhaps not that popular, & I believe had a different port configuration requiring a slight redesign of the piston, as this one I believe is a 1-yr-only piston. A guy used a 1994 KX125 head and a 1992-2002(?) C125R Honda piston and the 1994 ignition setup on a '97 KX125 bottom end with 1998 cylinder though, with great success. ThumoerTalk link will be edited in. 1999 was improved power over the unimpressive '98, and had a newer power valve configuration. 2000 had a heavier flywheel and more low RPM Power then any other 125 of this era as well as a strong mid-range, but feel a little short on the top and rev out of course. 2000 had the bladder forks, and some people said the chassis felt larger like a 250, although dimensionally it is nearly the same as a KDX in terms of wheelbase rake and trail. 2001 and 2002 were similar but had a lighter flywheel and less low end power although people still say in reviews that they pulled decent from the bottom compared to others of their class.

The 99-02 models all share the same plastics and with the last year to have the grab handle cut outs in the side plates EDIT - these look like grab handles, but a magazine test frim the period says they are actually just air intake vents for the airbox!. Not really a big deal with a grab handle strap being a bit better in some cases anyways, but I do like that feature. The side plates don't look as classic as the KDX or the 94-98 kx, but looking at the graphics on some of the factory bikes, they have a different color number background that is more rounded or ovalized which for me gives a more retro vibe and hides the fact that it has what I would consider a somewhat awkward looking side plate shape, although still better than the 03 and up which look like they are trying too hard to be different and futuristic.

2000 model team bike with great side plate graphics designs that give it a more retro look and distract from the slightly awkward shape of the plastics by giving the illusion of a retro shape:


The second one you can see the side panel shape a bit better due to the angle of the photo and the fact that unlike the first and third, this one doesn't have the stickers split between the air box exposed portion and the side plate portion adjacent:






I was previously considering the 2003 over the '04-05 because of the shorter wheelbase and shorter swing arm and more conventional linkage versus the more modern style on the 04+, but with a 27.5° steering angle and a lower ride height, the '03 lost favor with me and now I would more consider the narrow compact chassis of the 04-05 with their taller ride height and 27° steering angle. 26.5 would be more ideal, but this is close enough.
The 04-05 gained a fair bit of length on the swing arm I believe around 20 mm? But honestly now after someone gave me a reality check, I realize that the Beta 200RR handling that I loved so much actually has a much longer wheelbase at 58" but still that is reasonable compared to an awkwardly long 300cc in terms of how it feels and how the chassis is balanced.

Another guy was telling me that what he loved so much about his hybrid besides the narrower chassis and lighter weight, is the longer swing arm versus some years KX125 and all KDX200/220. Those 04-05 years still are not a substantially long wheelbase, I believe 57.2"? actually the same wheelbase as the '96-'97 KX125)
2005 engine had a few updates for longevity but no other major updates. The suspension linkage was changed as well although it's very similar to 04 but not compatible or interchangeable.

I still have a soft spot for the 96 stylings and the 97 model which is basically the same minus the purple and within improved swing arm (taller box section tubing) and an extra bearing in the rear hub.


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

Finding out that SKDA will custom design '96 style KX graphics for any Kawasaki model 1995 and up was also a big bonus.



They only show pictures of a late model 4-stroke KX models, but they will adapt the 96 KX graphics to whichever model you want even with some of the restyle kits. Basically if they have a template for the graphics shapes in their database, they will make it happen. This makes me feel more at ease as I am a sucker for the purple + checkered flag 1996 look....
I'll be browsing for a 2000 or 2004-2005 now, and perhaps a 2001-2002 & 1997 (or a '96 if it has the purple plastics!).




TFB Designs also offer 1996 style replica graphics to fit the 2003 and up KX 125 shrouds. I would have to get black shrouds or else maybe try to dye them in purple or just spray paint the plastic areas that are left exposed on the edges showing the base color.

https://tfbdesigns.com/product/1996-style-kx-graphics/


I also found out that the only currently available advertised 144cc 58mm pistons are Wisecos for 2001-2005+ KX125, and I believe they still need finishing due to the different intake port heights through those various years, so the intake port side is left uncut. They advertise center pinned, intake relief not cut out. All of the other years of interest have readily available 134cc 56mm pistons exclusive to each model year or years and not a universal fit to model KX piston.
The 134cc (YZ125) was recommended to me over a 144 by someone who worked extensively with Yamaha YZ125's, and I had also heard that the power valve may potentially be weakened on the older KX models by cutting them out to match a 58 mm bore, as well as the cylinder walls being fairly thin in regards to the coolant passages. The porting is more important than the big bore, so this is definitely not as much of an issue as what I would have originally felt.

Eric Gorr still has not updated his website since going semi-retired, but the preview says that he will no longer be taking on all of the custom customer jobs and will only be specializing in big bore kits from now on. I would be willing to bet that he may still offer the 58 mm 144 pistons for the 94-00 models.
On that note, I did see some discrepancies between Wiseco and Wossner as far as what year pistons were interchangeable. I looked them up on the Kawasaki parts interchanges but I have since forgotten my findings, but I did note that 1998 was unique to that year I believe. 99-00 I believe are identical, but Wossner I believe list it as 00-01 (if so, based on Kawasaki info, I believe that is a Wossner interchange error). Here I thought that the 1999-2002 bikes were all almost identical and had interchangeable parts! Apparently they were experimenting with the engines in 1998 and 1999 and had some significant redesign changes, yet all of the reviews online from the magazines did not care for the power characteristics of those years saying they were slow and not powerful enough.




I've also learned that higher compression cylinder heads will also boost low end torque and throttle response, but at the cost of requiring race fuel, was at the expense of high RPM rev out surprisingly!
I wonder how much I can boost the octane of 90 octane sheets not ethanol which is readily available to us, by using the VP Race Fuels octane booster, which I have been advised is the only octane booster that really works well.

A wider squish band also works with more low-end torque oriented porting, to get the mixture to burn best for the full duration of the stroke during woodsy midrange RPMs. Narrower squish band is best for high RPM power.
I went from wanting something that would run just fine on pump gas, to now realizing that it would be best to run at least VP octane booster + Sheetz 90 octane non-ethanol, if not race fuel.

From VB_Racing on ThumperTalk forum:
"My 2000 KX144 is going on its 3rd year now with zero problems. I built mine specifically for woods racing. I had it ported for more bottom end, and it is great in the woods. A LOT of torque, especially for a 125, *almost*, I dare say, KDX-like!! I would recommend my setup for anyone racing hare scrambles. Oh, and by the way, I weigh 190 lbs and am 6'1", so I am by no means a lightweight."


In other noteworthiness, all of the models in question have aftermarket clutch baskets from two or three manufacturers available. There was one basket interchange from 1994 through 2002, and the other was 2003-2008. The US did not get the 125 in 06, 07 or 08, FYI, but the 05 model was sold internationally as the 06-08 model years. Mitaka, Wiseco, and Hinson offer baskets for these.

Also related to woods riding, there was quite a long interchange of KX125/250 stators, so there is an aftermarket stator which includes a 35 watt lighting coil. These are not the KDX and 1993 and older KX style stators, these look more like a street bike stator with a full circle of many poles and windings versus a single pole stator like the KDX uses for both the lighting, and a second for the ignition. Unfortunately the aftermarket only offers a 35 watt lighting stator setup of this variety. The one stator covers all of the years I've been interested in. 35W good quality LED and good headlight reflector assembly and a DC rectifier should be adequate enough to get me out of the woods just fine if I get caught out past sunset, but definitely not with an incandescent bulb, LED-only, and no taillight, in order to conserve all the juice for the headlight. I would almost consider not even running a regulator after testing the voltage output, as I believe some motorcycle headlight LEDs will work fine up to 24 volts input. For purposeful night rides, it's always nicer anyway to have both the bike headlight and a helmet mounted LED light that is battery powered, so you can both see where the bike is pointed, and see where you are looking towards if you turn your head to the side or around a corner. So this isn't too big of an issue. Someone on one of the forums somewhere even mentioned that perhaps a KDX stator plate and flywheel rotor would swap straight to the 125 crank and engine case. That would take care of any flywheel weight desires as well as being able to run a higher powered lighting stator if needed.

Some specs:


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KDX200H/220R: wheelbase - 56.5" / rake&trail 26.5° & 4.3" / dry weight 223lbs (more like 233, no fuel, in reality) / seat height 36.2" / ground clearance 13.4"
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1995-1997 KX125-K2-K4: wheelbase 57.3" / rake&trail 26° & 4.3" / dry weight 191lbs / seat height 37.4" / ground clearance 15.6" (Wow! GREAT clearance for big boulders & logs!)
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1998 KX125-K5; wheelbase 57.7" / rake&trail 26° & 4.3" / dry weight 191lbs / seat height 37.2" / ground clearance 15.4" (Wow! GREAT clearance for big boulders & logs!)
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'99-'02 KX125: 56.5" wheelbase / rake-trail 26° & 4.3" / dry weight 192lbs / seat height 37.2" / ground clearance 15.4" (Wow! GREAT clearance for big boulders & logs!)

So... these actually have a STEEPER steering rake @ 26° vs the KDX @ 26.5°! This is the year with the heavier flywheel and more mid range torque oriented porting than most other years... This seems pretty appealing although Motocross reviewers from magazines at the time said it felt almost as big as a 250 despite the numbers saying significantly otherwise. The swing arm was 20 mm shorter than the 250 and the head tube was pulled back 15 mm versus the 250. I think it might be related to triple clamp and handlebar ergonomics, the feeling of it being a bigger bike. I'd be inclined to try 1998 RM125 49mm Showa Twin Chamber conventional forks on it for sure then along with the KYB bladder technology that some did not like.
This is a 2-yr-only piston although readily available
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2003 KX125: 57.2" wheelbase / rake&trail = 27.5° & 3.9" / Dry Weight 192lbs / seat height 36.6" / ground clearance " /
(so it seems that the 2003 actually may not be necessarily what I would want of steering rake, 27.5° with a low seat height -vs- the 2004-2005+ KX125 @ 27° with more trail & taller seat - I could lower the forks in the clamps alightly and get back down to 26.5° again & have greater trail (more triple clamp offset which also contributes slightly to the longer wheelbase spec).
------------
'04-'05+ KX125 = 57.9" wheelbase / rake&trail = 27° &4.4" / Dry Weight 192lbs / seat height 37.2" / ground clearance 13.4"
This actually could work out quite well with the front end dropped slightly to get nearer to the KDX & older KX125 steering rake angle, and also running the chain a link shorter to have the axle slammed forward, still a longer wheelbase to help with the steep hill climbs but not as awkwardly long and lazy as a 250 or 300...
------------


In light of reviewing all of the geometry specifications, the 2000 model definitely seems like a huge consideration especially with the cylinder porting and the heavier flywheel, and perhaps an 01 or 02 could be ported similarly after port timing lowering / advancing through cylinder base milling, + a 96-98/99/00 head, and flywheel weight added, if I found a good deal. '99 as well. I think now I've got a pretty extensive understanding of the differences between the various years in regards to what I would want for a Woods bike build, so now I probably have enough information to call Tom Morgan on the phone and talk to him about what year is best or how we could mix and match cylinders and heads. And '01-02 cylinder fitting the 144 piston with a modified 96-98/99/00 head could definitely get me what I wanted as long as the cylinder porting were conducive to alterations for more low-end torque after base milling.

I just checked out '96-'98 vs 1999 vs 2000 vs 2001 KX125 cylinder heads, with some interesting findings, significantly different tunings each year.
The 1999 KX125L1 cylinder head looked like a KDX220SR, with a VERY WIDE squish band and small dome. The street legal KDX220SR was designed to run lower RPMs.
The 2000 KX125L2 cylinder head looks to have a squish band width similar to a KDX220R (medium to slightly wider, for a very strong mid-range and a decent bit of low torque),
The '97 ('96-'98?) KX125K4 had had a fairly wide squish band about the same size but perhaps just a bit wider than the 2000 model KX125L2, but not nearly as wide as the extra-wide '99 KX125L1. ***Update*** another one that I found that had the same casting number 1435 stamped into it, had a much wider squish band like the 99, but the first one that I looked at and initially commented on for the 97 came from a bike with a Tom Morgan Racing sticker on the fork, so I'm wondering if this head was swapped for a 2000 head on a 97 model bike perhaps, as a tuning tweak? 96-98 share the same head part number though, on the Kawasaki diagrams.
whereas the 2001 KX125L3 seems to have a much narrower squish band width similar to a KDX200, and a larger dome to have slightly lesser compression, both to focus on more peak high RPM power.

Very interesting findings I was thinking I might just try and snatch up a 2000 cylinder and head if I find a good deal, and then I could run any model year 99-02 if the crankcases are same on 99, but now I'm seeing that there are a lot of options of mixing cylinders and heads, but the 96-98/99/00 heads would be the ones to run for low and mid-range power....
Some of the years would need more extensive cylinder base milling and cylinder porting work for woods torque, where the 2000 would need only a basic port clean up and boring to 134cc/56mm.
The 2001-2002 can run the same Wiseco piston as the 03 and up, and have the semi custom off-the-shelf Wiseco 144cc 58mm pistons available.
So really for my goals, modified 96-98/99/00 head bolted up to a 2001-2002 cylinder with whatever crankcases I'm running port matched to the cylinder I'm running, cylinder bored to 144cc, might be the best option, although requiring more cylinder base milling to get the port timing back down for low-mid torque... That extra 2mm bore to add 10cc extra definitely sounds appealing.... As do custom KDX144R swingarm graphics!

I'm speculating that the main differences in the pistons were to suit the different years of cylinders and their different porting configurations, the best I can guess. Don't take that as fact though.

The cylinders should interchange as long as the transfer ports are matched to the crankcase, but it does seem they were a fair bit of differences in the transfer port and base gasket configuration to suit? I do know someone built up a 96 or 98 using a 2000 cylinder with only minor transfer port matching on the cases to cylinder required. The head gasket interchange 1994 through 2002. The 2000 base gasket, crank cases, and cylinder are all unique to that year, as well as the head. Maybe a '99 for a cheap deal would even do good if I could swap on a 2000 cylinder and head, bored to 134cc, with some low-end torque oriented and mid-range porting.

'99 and 2000, maybe '01, have the oddball u-shaped DID rims which crack. The DID Dirt Star / Excel Takasago standard style rims are a lot better, but the OEM versions are a lot softer than the aftermarket or the top of the line aftermarket versions of those anyways so I guess it's not that big of a consideration.

The ground clearance on the 96-02 is EXCELLENT. The 96-97 model might be quite appealing with its higher ground clearance, slightly longer swing arm than a KDX, taller seat height, and thicker seat foam. I could shave the seat foam down slightly to save a little weight and lower the seat height, but still have almost 2 inches higher ground clearance than the KDX... Even with adding more sag to the suspension spring preloads, with its squatting a bit, I would still have more ground clearance than the KDX for the 03 and up KX... As much as I have loved that 96 stylings and plastics of that generation, the 99-02 is actually really growing on me now after seeing some attractive graphics that make the side plates look better, pictured above, and the ability to get '96 style purple/checkered flag shroud graphics for it....

I did a real bad thing just now and started browsing marketplace for KX 125 for sale for cheap.. luckily I didn't find anything, the wife would kill me at this stage! I need to move some other bikes first.

Although the resale value would not be anywhere near my investment versus buying an Austrian 150 and just running it mostly stock, I don't want to run a KTM at all because I want a linkage rear suspension, and Husqvarna 150's do have the linkage suspension at least the most recent models, but I still don't care to ride an Austrian bike as everyone rides in Austrian bike and I am partial to the Japanese bikes.... The Italian sure seem to be cranking out some great bikes with the TM EN144 and the Beta 200RR Race Edition, which definitely get my consideration, but I am a tinkerer even if it's the death of me, and I prefer to build something out of these vintage bikes with the retro purple '96 checkered flag graphics and green Kawasaki colors throughout... Plus, Kawasaki, KYB, and Showa are what I know & love!

Some GREAT INFO here:

https://www.vitalmx.com/forums/Old-Scho ... fo,1279889

"MadMatt579
1/9/2015 3:26pm
(for a 94-98 vintage to fit '96 & earlier class rules,) I'd go a 96 if you can find it. Less flex 46mm forks and the mid valve which when setup properly is a great fork. Ive got mine working really well after I resprung and revalved it.
I also revalved the shock to 01 specs which works great also. But that's on the 97 longer swingarm though. (is it really any longer?)
Couple issues on the 95 (my first new bike). The power valve actuator was changed to have a two step design. Sometimes the centrifugal force doesn't get the balls over the second step and doesn't open the power valves fully. 96 changed it back to the 94 smooth version. But you can just swap out the 95 for the 94 or 96 version.

95 also changed the linkage so it firmed up in the latter half of the stroke but it made it a bit too harsh. 96 changed back to the 94 linkage.

The drum power valves need to be matched to the ports. Mine was blocking about a 1/5 of the port and made a good difference to the top end when trimmed.

The FMF Fatty works very well to beef up the power curve and give a bit more top end.

Run a Honda CR front master cylinder to improve the brakes. Even my 97 brakes which were improved were not as good as with the CR master cylinder.

so 95 PV and rear shock linkage have some issues... good fork for KDX swappers though, so I could run one of my '98 RM125 forks swapped and have no qualms! '98 seems to be an oddball year for engine top end parts, so I think I'd swap a 2000 or 2002 cylinder and power valve parts onto the 98 cases and do whatever required port matching is needed.

"RyanLester761
1/13/2015 8:56am

The '95 had the 35mm carb and two-stage powervalve cup (as stated above)- slow and hard to keep on the pipe.

The '96 had a good low-end bark and decent midrange, but ran flat on top. Good holeshot potential on short starts.

The '97 runs a lot like the '95, hard to keep on the pipe."



"Kidkawie
1/6/2015 5:33am

I can't comment on the engines, but for the chassis:

94 43mm KYB's no mid valve, frame welded brake pivot tends to wear out, frames are like glass.

95 and 96 chassis basically the same, new removable brake pivot, 43mm KYB's with mid on the 95, 96 get 46mm KYB's. New front number plate in 96.

97 and 98 redesigned swingarm, wider pegs. garbage progressive stock fork springs, 3 rear wheel bearings.

Cranks can be difficult to find. Look to send it out for a rebuild.

If you're trying to determine pre-96, the 97/98 dead giveaway is the fat swingarm. Anyone who knows those bikes can spot it from a mile."


"The Sneak
1/8/2015 6:18pm
A few yrs after I quit racing, I borrowed a 97 KX125 that had been raced the previous year at Loretta's (mod class). FC suspension set up for a kid 20 lbs lighter and light years faster than me.

I really liked the bike other than it was slower than a stock new 99 YZ125... Now this bike had a ton of hours and had been used as a practice bike since...so I have no idea how well they run.

I found it very stable and liked the ergos much more than my old 1993 YZ."

"Jeekinz
Posted February 15, 2012

What makes the K model brakes better?

Something with the master cylinder. My 98 had excellent brakes, not sure about the 99's but the 2000 front brakes just plain suck. You have to swap out the front master with one from a 05+ KX (any model big bike)."



AND THIS THREAD IS PURE GOLD!

https://www.thumpertalk.com/forums/topi ... 125-build/

He basically says the '02 has the best power valve top end setup of all '94-'02 engines, and has details how to swap newer cylinders 01-02 onto the 98-00 cases - "The 01-02 motors use rounder transfer tunnels and they opened up more area in the cases to feed the rear transfer ports."

"The 94 KX had a flat top piston which I like, and since I have a flat topped head off of that 94 motor I opted for a 92-03 CR125 piston. Clearly the deck height is different, the idea being to run the pre-98 106mm rod with a 1998 cylinder. The 97 and earlier KX125 uses what I consider a bizarre porting and power valve design. It has a bridged exhaust port like the later engines but also has two sub-ports on either side of it. This means two three piece exhaust valves in the main exhaust port and two drum valves in the sub ports, in addition to all of the associated parts to make it all work. All of this stuff is discontinued and its all worn out. The 98 and later 125 motor uses a simplified port and power valve design with a wider bridged exhaust port and an all steel three piece power valve. No drums, no gear teeth to wear out. This is a 99-01 valve but the 98 is similar:"





At this point, I'm leaning towards a 1996-1998 bike, and the later cylinders have a bit better design, especially the 2002 power valve (although I'd have to have the base gasket surface turned down to drop the ports for better woods torque port timing). The 1995-1997 cranks are harder to come by as well, and the 98-02 cranks do not interchange backwards to 95-97 or 94-97. Seems best if I'd fit a '99-'02 bottom end into a '97, or a purple '96 with the '97-'98 KX125 swingarm and 99-02 top end (preferably 2002) and 98-02 bottom end...Or else get a '98, and swap an '02 cylinder onto it or a 2000 cylinder and head. 2001-2002 can go Wiseco 58mm for 144cc, whereas this 01-08 144cc piston is not advertised for the older models which have a max of 56mm 134cc pistons currently available.

If I got a 1998 bike, I'd want to swap out the top end for a 2000 or 2002. 01-02 also have the ability to get 144cc pistons for them, so the 2002 top end is really the most ideal cylinder and power valve componentry. Cases have to have some transfer port matching done for 01-02 cylinders onto the 95-00 cases though, but no big deal.

One KX hybrid builder has said here and elsewhere that the slightly longer swingarm of his KX125 chassis (meaning not a 99-02 or 03 as those are same wheelbase as a KDX) is one of his favorite parts of the hybrid chassis.

I'm still open to a 2004-2005 as well, as the narrower chassis and most updated engine is definitely an advantage, but the 94-98 stylings are definitely still my top favorite... I'll just have to do some fab work for radiator guards and skid plates on the 96-98 chassis.

No luck finding a '95-'98 or even '99-'02 KX125 for sale at the AMA Vintage Motorcycle Days Festival & swap meet, but I saw a bunch of '94-'98 KX125's, none for sale. Also of note, chased a kid around on his '99 or '00 KX125 & was surprisingly impressed with the low-mid grunt out of tight corners on that thing, especially after rippin' it hard on my brother's '00 CR125R which has ZERO bottom end but is a SERIOUS top end screamer, to what felt like 13500-14000 RPM!!! Terrible woods engine as stock but Eric Gorr is producing aftermarket cylinders for that era CR125 now!

'97-'98 KX125 is my goal, & today I found one for sale with the top end apart for $1500 1hr from me.... There may be better deals to follow though, & I have zero space for another bike until my buddies' bikes are out of my shop

Tell them to make plans to get their stuff gone. :-)

KDXGarage wrote: 06:45 pm Jul 29 2024 Tell them to make plans to get their stuff gone. :-)

Well... I'm the one repairing them, or supervising the repairs! That takes two to get them gone!

I also need to rebuild my KLX300 forks to sell, & revalve the midvalve+ new seals on my '97-'04 KX500 forks, which I may also sell in favor of this stack of '98 RM125 forks that I've been hoarding! 49mm Showa Twin Chamber right side up forks!





So I'm looking at either a '98, or perhaps a '97 (or a '96-'96 + '97/'98 swingarm) for the 2mm longer connecting rod (same as KDX200?) possibly with the better port/powervalve design 98 or 99-01 or '02 cylinder, but with a 2mm shorter 1992-2003 CR125R flat top piston, and a '94 KX125 head to work with the flat top piston... Longer rod for less side loading for improved longevity (it was likely shortened for higher rev potential????), & 98+ better powervalve design. 2000 model year flywheel as it's the heaviest. CR125R pistons are available in 57.00mm as well, for 139cc - many people have told me it's not as ideal to take a 125 out to the full 144cc 58mm overbore, so perhaps a 57mm 139cc +3.00mm overbore will be a bit more reasonable? I think we're getting somewhere here!
The others will do as well, a '98 bike (98-02 bottom end) with the revised shortened rod should also produce great results, but I'm looking to maximize longevity and midrange grunt. I'm pretty decided on the '95-'98 (skipping '94, the 1st year of the K-series, as '95-'98 received so many improvements) generation as my platform now. 99-02 is quite excellent but same exact wheelbase as the KDX, 97-98 are just slightly longer, but not by too much! Better classic stylings as well. Better parts availability on 99-02 OEM & aftermarket, tanks & radiator guards & skid plates.... I can make do on those though!



I might start shopping for a few more parts for this like an AC Racing aluminum seat subframe (99+ had aluminum subframe stock), & a 2000 or 2002 cylinder and powervalve assembly.
Still undecided on rod length, but wondering if the 94-97 rod can swap to the 98+ cranks to run the '94 head and 139cc CR125R Wossner pistons???? Same crank pin part # & same big end bearing! Different thrust washers.

TBC

Jeekinz used to make a lot of posts on the KX125 from somewhere in that era of models. Search and read.

Sounds like you have it narrowed down pretty good.
I never really had any problems with my 97 off-road, power wise. Idk? Seemed to work for me, but I didn't do much rock hoppen eather...
That being said, a big bore would have been even better...
If you have any questions, Ill try to help.

There's apparently a huge difference between the 94-98/99-02 engine traits vs the '03-'08 KX125, which has traits closer to my brother's '00 CR125R with zero bottom end and almost no midrange grunt, but insane top end 5500-12500rpm power... I'm definitely looking to go big bore 134cc on any year 95-02, or perhaps '95-'97 long rod + CR125R 57mm 139cc piston + '94 KX125 head + 99-01 or 2002 cylinder... + "more power everywhere " type porting with an emphasis on low-mid grunt perhaps? I suspect what I'll end up with will be an ultralight woods bike with as much torque as a KDX200 at least, which will make me less likely to take out my beloved KDX220!

I'm already brainstorming cutting up an H-Series KDX frame & KX125 frame to add a 99-01 KX shock mount (higher up vs KDX) + attachment points for an aluminum KX125 '99-'02 seat subframe, and TIG welding on subframe mounting points for KDX seat and side cover number plates.... Add to that all my titanium parts, and the torquey 220 with RM125 Showa suspension may be equally favored alongside the "KX134R" or shall we call it a "KDX139R?"

If I built a hybrid, I'd be looking at how the KDX fuel tanks might possibly fit into the '95-'98 or '99-'02 KX125 frames, as welding on different shroud and radiator mounting points to the steel KX frame would be simple, and the KDX engine cradle swap is simple into these eras of KX frames. I'm uncertain how the KDX seat would enter that equation on the '99-'02 KX frames (higher & thinner seat), so I suspect some '99-'02 KX seat pan reshaping might be necessary, and running KX rear plastics and airbox.

On my 97 kx:
As far as the airbox intake s under the seat, they make a great place to grab. I find it easier than the strap I installed, but options...
The seat is actually pretty comfortable. Not as much as the kdx of course, but still nice on longer rides.
I did consider the kdx tank, but it's to wide to slide into the kx frame. I'm sure you could make it work with some heat, but I think modding the stock tank would be easier, with heat/air like you mentioned before. Looking at mine, I think 1/4 gal or maybe more should be doable. 2.25gal stock.

I was browsing a bit today and noticed that Phathead Racing happens to make a bunch of heads for the KX125's '98-'00, '01-'02, & '03-'08, with 4 different inserts available for each head generation, mostly differing in volume / compression / required fuel octane.

and... THEY COME IN PURPLE ANODIZED!!!!
(as well as a few other colors Gold, Black, Blue etc)


https://phatheadracing.com/search?q=KX125

They don't list anything but stock bore, but Luke @ Phathead / Luke's Racing said they can do any custom setup possible within reason, and said that the stud spacing is too close on a 144cc overbore on 94-02 KX125's to be able to use an o-ring'ed head like all theirs generally are, and you must use a stock type head gasket if doing a custom 144cc bore head insert.

In addition to their different dome volumes advertised, they can do different squish band widths and bore sizes upon request, but these aren't advertised due to many variables and needing to consult at greater length with them.




He said on the redesigned 2003-2008 KX125 engines, a 144cc overbore is able to be o-ring'ed as their stock bore heads are.
The sole 144cc KX125 +4.00mm piston available (Wiseco) only shows fitment for the '01-'02/'03-'08 port configurations anyways, but it sounds like a 134cc Wossner piston setup is the best option of going with a '98-'02.

I still haven't found a smokin' deal on a bike needing rebuilt yet, but I'll be watching... I've got plenty of projects to keep me busy for years, but this pipedream keeps near the forefront of my immediate interests. A '98 is probably my primary interest, the older stylings but newer crank and rod length, newer cylinder compatibility with 98-00 bolting on with appropriate power valves, and '01-'02 fitting with some transfer port matching and the same year power valves.

Even if I found a 2000, 2001, or 2002 complete bike, apparently the 94-98 subframe boots straight on with all the back end parts, and with some tabs relocated, the older shrouds and tank eyc will fit on the frame... A custom "Classic Restyle Kit" going back a generation instead of making a cool classic look like a modern bike...

In my watching of Chris Simmons' (husky250 on here) videos which are mostly on his '88 KDX200, I again was reminded of how much lighter & more nimble the '86-'88 KDX200 is vs an H-Series or even E-Series...
With the slower technical riding and log hopping and boulder hopping being an area of riding which I gravitate towards, the extra 64cc's displacement of a C-Series air cooled KIPS-equipped KDX200 generation (versus a heavily modified 134cc water cooled KX125 woods ported engine) would most likely be an advantage that a bored/woods-ported 134cc engine could not surpass in terms of torque and catering towards my riding style with lugabilty in mind.

I'd love to have an '86-'88 KDX200C & swap RaceTech equipped Honda XR400R forks and perhaps an '85-'87 (?-ish?) KX swingarm for disc brakes...

Alternatively , instead of a disc rear swingarm swap on a KDX200C, swapping a KDX200C engine and gas tank into an '88-'89 KX125 chassis with the same Honda XR400R/'97-'99 DR350 Showa 43mm gold forks in the '88 KX triples (or berter - the Showa 46mm versions from a '95-'99-ish RMX250 into '89 KX triples) would be quite an incredible lightweight woods machine...
Same classic side panels on those as the '89-'04 KX500 / '89-'94 KDX200E, + air cooled 200cc KIPS engine + the 125's aluminum seat subframe. This combo could very well bump my '98 KX125 pipedream out of the "next project bike acquisition" spot!
Add some frame hoops and a SxS skid plate / linkage guard for the H-Series, Tubliss, & later Honda CR front brakes + stainless line, & this could really be another ULTIMATE classic woods bike formula...

Either that '89 KX125/KDX200C hybrid or else a KDX200C + rear disc conversion + 43mm 1998-ish Showa forks with the full titanium fastener treatment & high compression cylinder head + cylinder porting could really turn into the ultimate ride for me all-around... I'll see how my full titanium treatment + aluminum parts weight reduction fares on the KDX220 this coming spring first though, but a lighter weight woods bike is always a favorable direction to desire, and one that is more luggable with 64cc's extra will definitely be more appealing...

Can anyone with experience in both the '86-'88 KDX200C as well as KX125 porting & 134cc big bores perhaps comment on potential power and torque between a ported high compression head '88 KDX200C vs a 134cc ported high compression KX125?

I could perhaps see the '88-'89 KX125 as an excellent chassis platform for my gearhead tinkering tendencies. Center spine frame, so I could most likely modify it slightly to mount an air cooled KDX gas tank and '86-'88 KDX200 engine and pipe, or also perhaps run a KX500 tank+shrouds+seat+radiators, & stuff a KDX220R engine in there with probably an E-Series KDX200 Pro Circuit pipe.... KX500 linkage bolts and swingarm pivot bolt as well, or course the titanium versions!

This is sounding quite appealing. I'll definitely be trying to sell my Suzuki PE175 (& maybe PE250) to fund this endeavor.... hoping to sell off some of my vintage Suzuki GS750/1000 street bikes and engines as well, as I seldom ride them except for a motocamping / twisty roads riding trip 1 or 2 times a year., as enduro riding and hard enduro have pushed street bike riding aside...

Chuck78 is the Dr. Victor Frankenstein of the KDX universe!