97-04 KX500 / 96-97 KX125/250 swap - height & valving, vs KLX300R

Questions and comments about converting to beefier forks..
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

Check and see if RT says to install a check valve instead of the midvalve.

Going the RT way sounds good for you.
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KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

I suppose my biggest questions are in whether or not I could use the stock 97+ KX500 valving piston & achieve the same level of plushness and overall good well balanced performance as if I used a RaceTech Gold Valve kit?

I would think that the RaceTech might ultimately give a bit better ride quality and broader range of tuning, but perhaps one could not tell the difference between it and a Racetech valve if both were very well dialed in?

The fact that there are so few valving shims in the kx500 base valve made me think that probably what was stated is the case, that the piston is fairly restrictive compared to the KX 125 and possibly 250 (& similar Yamaha KYB fork model piston that one member swapped in place of his KX500 piston), and that (the piston orifices) controls a fair bit of the damping as well. The other scenario would be that they did de-tune the kx500 in it's last 8 year run when there was no longer and open class Motocross two stroke contingent; & that the kx500 would have been targeted more for experienced trail/desert riders at that point?? And hence the damping was softened quite a bit? I don't ever recall seeing it marketed as a trail bike in later years, but I was in college then and was basically 24/7-365 obsessed with BMX bikes/dirt jumping only...


So the greater question is... what to do with the mid valve???? Tune it? Disable it? If using the stock piston, I'ddefinitely be trying to tune the mid valve, but if Racetech recommends base valve settings solely based upon disabling/removing the mid valve, then that may be the easier (but unfortunate???) best plan if going RT.

Thanks Jason!
I think I will probably be buying your rear shock rebuild kit tomorrow, have to make sure the boss lady doesn't spring any other financial needs on me 1st, though.

Once I build up this spare engine, the forks will be the next project on the bench for myself...
In between carb jobs on a 77 GS750 & 78 GS550 for friends, KX250D fork rebuild, & 74 Rickman Montesa 250 MX carb rebuild/ignition upgrade/beater bodywork swap. Short seat height cool old bike for the 5'2" lady to cruise on so she doesnt always feel left out when i hit the trails... :grin:
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

You have a lot of projects. :grin:

Thanks for possible buying the shock kit. I think it's a great kit.

For ease of use, going with the Race Tech kit is going to get you a lot closer to how you want it than re-re--doing the stock stuff. You may need to buy additional shims for the stock stuff, whereas the RT will have what ou need all in the bag.
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

Jason wrote:You have a lot of projects. :grin:
Every bike I have is a project... 9 total street & dirt, plus the boss lady's 1977 Suzuki GS550... I don't count her 86 Harley as a project of mine because I dread wrenching on Harleys, & particularly despise them...
Plus at least 5 bikes of "friends" that I have adopted in order to keep them safe& continue to have more riding buddies with working bikes to go out & have 2-wheeled fun with...

Out of my 9 bikes, always keep 1 street & 1 dirt bike in top notch riding shape. The others are in various states from needing a few thing, to 1 bike that is a titled frame and crates of parts...
My winter projects will be 1 other Suzuki GS (GS425 489cc racer? 740cc GS550? 1135cc GS1000?)
And... the 1977 Suzuki PE250B (PE = "Pure Enduro") with 78.5 RM250C2 rear end with Fox Factory Shox, '83 DR250/Racetech front end, & all the period mods I can squeeze, maybe even a Lectron flatslide. Ported cylinder, Wiseco, pipe, Tubliss + MotoZ Arena Hybrid Gummy + Shinko "Goldentyre" 216.
Hope to start some vinduro action at some point. I missed AMA Vintage Motorcycle Days this year (camped/partied/spectated only).
This will be one (side)step beyond my dream of an 88 KDX200 primary trail bike. Far more vintage (as old as it gets while staystaying the long travel i.e. rideable range), so I'll keep my 99 220 as the mule unless I find a titled 88 KDX200 or an 86-87 with an 88 carb or other upgrade carb. From what I gather the 88 was 1-off year carb body with the mixture screw & choke on the opposite side from all newer variants.


Jason wrote: For ease of use, going with the Race Tech kit is going to get you a lot closer to how you want it than re-re--doing the stock stuff. You may need to buy additional shims for the stock stuff, whereas the RT will have what ou need all in the bag.
So I read the Race Tech instruction manual for the gold valve kit for this style of KYB cartridge fork. It made very little mention of anything with the mid valve whatsoever, other than saying that there are two or three additional specialty tools needed if you want to change the mid valve or rebound valving. So I'm hoping that with their online custom tailored valving specification worksheet, it tells you what to do with the stock mid valve. Either tune valve for it, or how to tune the mid valve as well.
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

You have a long list indeed. :grin:

Look around Google search to check the float distance on the midvalve. I don't know if someone has a post on it here for sure or not. There might be one. I have not fooled with it in a while. I Want to say it is the distance between the valve and shims without the spring, something like that.

I know that is one thin that theory has changed on since 20 years ago.
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KX125 or KX500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

So this is question is not about my bike, I've gotten 97 KX125 .38kg springs & Racetech gold valves, & need to install them with this Pivotworks fork rebuild kit.




For my friend's 92 KDX250 (245lb dry weight + 180lb rider) with a damaged fork tube, I'm looking at:

1st generation USD KX125 43mm KYB "blue" forks that originally were equipped with .37kg springs.
vs
93-96 KX500 forks that were originally equipped with .40kg springs.

Racetech spring calculator says for a beginner trail rider age 30-44, .37kg spring is good.
For a C level Novice, .40kg is good.
Brent the bike owner was amazed at how the KDX just eats up huge bumps like nothing... he was afraid to go too stiff and lose that capability, but i wondered if softening the valving woukd be plenty to keep it plush with the. 40kg KX500 springs?
These forks are silver & would look better in my opinion as well.

Is there any advantage to the slightly newer 500 forks over the blue 1st gen USD KYB's? They are only a few years apart but potentiality there could have been significant piston/valving design changes.

Do you all think that with a softened up compression stack, that the .40kg springs on the heavier KDX250D will still give him a very plush ride?

Is .37kg too soft for his weight and the slightly heavier KDX250? I used a 95 kdx200 (220lbs) & 200lb rider input to check that the RT calculator database wasnt just mistaken on the 250's weight, & I got the same recommendation. .39kg or .40kg for C level Novice.

If he gets the blue forks, he'll have a spare set of triples, so someone could possibly use those to upgrade their 95+ KDX to 43mm USD KYB's since the KDX250 triples already fits several Kawasaki 43mm USD KYB forks.

Thanks!
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

Go KX if his budget allows.
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

Jason wrote:Go KX if his budget allows.
YES! No luck getting a KDX250 right lower/inner fork tube, even including all the complete sets, all the right sides had problems with the chrome!

The question above was about the 1st gen 1990-ish 43mm blue KX125 forks vs slightly newer KX500 forks 1993-1996

What are your opinions on the blue 43mm 1990-ish KX125 USD forks (.37kg springs stock) vs the 1993-1996 KYB 43mm USD KX500 forks (.40kg stock)?

Is there a big technical advance in the 1993-1996 KX forks over the blue 1st gen USD 43mm KX forks?

180lb rider 243lb 1992 KDX250D
Racetech says:
.37kg for beginner trail rider
.39kg for C-level Novice
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

OK, 1990 KX125 / KX250 / KX500 forks are not going to fit into his tubes and would be 41 mm chrome inner tubes, so that is a touch less rigid than anything newer.

As far as KX goes, 1991 - 1993 KX500 forks are all about the same as the 1991 KX125 / KX250 forks. KX500 forks did not advance until the 1994 model. 1991 - 1993 are all blue. 1994 and newer are not blue.

1996 KX500 may have the midvalve like 1995 KX125 / KX250. Otherwise, I would be more worried about mechanical condition over what is inside anything between 1991 and the midvalve forks.

In other words, I would rather have better condition earlier forks than later forks in the pre-midvalve years.
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

My apoligies, they are 1991 KX125 blue 43mm forks... .37kg springs were stock.

Vs 1995/1996 KX500 43mm forks that should have had .40kg springs stock.

They both should slide into the KDX250 triples.

Aside from spring rates (which could be non-stock by now anyways), is there any big benefit to using the 95/96 KX500 43mm USD's?

Thoughts on new trail rider @ 180lbs+gear (5 rides now, avid street biker and well versed mountain biker - the pedaling non-motorized kind) on a KDX250 with .37kg vs .40kg springs?

Thanks Jason and everyone here,

Chuck in Ohio
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

Chuck78 wrote:My apoligies, they are 1991 KX125 blue 43mm forks... .37kg springs were stock.

Vs 1995/1996 KX500 43mm forks that should have had .40kg springs stock.

They both should slide into the KDX250 triples.

Aside from spring rates (which could be non-stock by now anyways), is there any big benefit to using the 95/96 KX500 43mm USD's?

Thoughts on new trail rider @ 180lbs+gear (5 rides now, avid street biker and well versed mountain biker - the pedaling non-motorized kind) on a KDX250 with .37kg vs .40kg springs?

Thanks Jason and everyone here,

Chuck in Ohio
I don't think there is going to be a big difference. Whatever it is, it probably won't be noticed by the rider. Just shop for condition.
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

Thanks buddy, much appreciated.
He wanted plush, to continue being able to soak up monster bumps and big rock shelves. Starting with his very first ride, I coerced him into doing some hill climbs that he was uncomfortable tackling, which after he had made it up, was just blown away with how much the suspension will eat up the big rock shelves and steps on some of our steeper and more rugged hill climbs in Wayne National Forest. He does not want to lose any of that ability to just cruise right up some really rugged-looking stuff that would have previously scared him, and we dont want him having any compromised traction due to bouncing off of rough parts of the trails. He is definitely not motocrossing. We can always get stiffer springs later or find a wrecked set of 250 or 500 forks just for the springs.

When doing new seals and oil, I will evaluate the base valve compression stack and probably remove some of the bigger spring shim washers to make sure we can get his compression really good with the clicker screw near the middle of it's range.




FREE KDX--->>>KX 43mm USD fork swap parts sourcing tips below!

I did a lot of research to find the whole front end to swap. If he gets these KX125 forks, they will have triples that will bolt into any KDX basically, and he is still ablke to use his KDX250D triples as they will fit the forks also. I will post up eBay links for the parts that he did not choose due to wanting a very soft spring rate (KX125).
It was actually very difficult to find a usable condition good eBay wheel that I was okay with purchasing and mounting a tire to, out of maybe 120 or more that I looked at for the 2 different generations of forks/hubs/axle spacers. So I will post links to the KX 500 forks that he does not buy, and the matching KX wheel and axle, and he will have a set of triples available for sale that will bolt straight into a KDX frame. So someone else can reap the benefits of a few hours of me scouring eBay for a good KX swap candidate parts packages.
There was another cheaper set of silver "95 KX500 forks" listed that were not KX forks as best as I could tell, no rebound adjuster on top cap, only bleeder screw! KLX?

Thanks everyone, thanks Jason!

Chuck in Ohio
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

If he is wanting KDX plushness, you will definitely have to revalve KX forks.

Did you pass on these:

https://www.ebay.com/itm/1991-94-Kawasa ... SwqH9bcyE5
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by Chuck78 »

Ahhh... no i had not seen those!
At this point, even though it means more work for me, I think I will have him just go for the blue 43mm 91-93(?) KX125 forks since I have done this much research into it already, and ultimately it will be the better choice, more flexibility, and make the bike have greater value if he sold it. That, and swapping to a leaner carb slide and jet needle, as well as already installing a Wiseco piston and thinner KX250 head gasket... now I just have to convince him to get an aftermarket expansion chamber and fresh rear tire! And a Leatt 5.5 Pro HD chest protector or body protector! He really banged up his shoulder when he crashed in some big rocks after crashing avoiding a head on collision 15 minutes before...
Then his bike will be really really awesome all around...
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

I suggest you look into the KDX250 forks I linked to. It would be a lot less hassle to get the bike up and going again. KX forks are not going to bring a lot of resale value to a 27 year old dirt bike.

No need to buy an axle and wheel, worry about travel being too long, etc.

Save yourself a lot of work and just get them. :cool:
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Re: KX125 or kx500 swap - heights & valving? vs KLX300 swap

Post by KDXGarage »

This might help. I put the stock "stack" on the KDX250.

http://www.kdxrider.net/forums/viewtopi ... 02&t=21675
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Re: 97-04 KX500 / 96-97 KX125/250 swap - height & valving, vs KLX300R

Post by Chuck78 »

Here's some fork swap info I dredged up from multiple places and compiled for easier search success, this is info on fork swaps that DO NOT require pressing out the KDX stem to swap into the donor triples with machine work etc, these are all bolt-ons.


KLX300R forks are the easiest swap, as they are valved similar (but better) to the stock KDX fork for woods, are a fairly correct height without mods (they're actually 11.2" travel vs stock 11.4", and similarly around the same amount shorter height as that vs stock KDX forks sprung for your weight), and come with a decent spring rate for a lightweight 138lb-160lb woods rider at .37kg/mm. KDX wheel is a direct fit into these forks without any axle adapters. These are still the same cartridges and tube diameter as the stock KDX right side up "conventional" forks at 43mm, but they are significantly less flexy than the KDX forks due to being inverted. These are lacking the full external adjustment that the KX forks have, unfortunately, but come valved pretty decently stock, so these are absolutely the easiest upgrade with almost no hassles whatsoever. I'm riding a pair of these in extremely rocky Southeastern Kentucky / Southern West Virginia trails as often as I can make the 3.5-5 hour drive, and they feel so much better than the "better" WP 48mm forks on my wife's '07 KTM 200 XC-W. Her bike's valving and spring rates gives me a headache to ride aggressively fast (30-35mph on the faster bits, never topping 40mph) more than a half hour on this gnarly rugged rocky terrain at Redbird Crest (amazing medium difficulty trails in Daniel Boone National Forest) and Buffalo Mountain/Devil Anse and some riding at Rockhouse (all areas of the Hatfield-McCoy Trail Systems, mild logging/gas/oil road trails up to the hardest pro level singletracks you could find).

1988+ KX500 use the same steering stem length and bearing sizes as the KDX (all KDX models 1986+).
1988 are conventional 43mm cartridge forks
1989 are a 1-year-only 46mm conventional cartridge fork (sounds like a great fork to revalve for woods riding)
1990-1996 are 43mm inverted cartridge forks. I believe some of the later years there have a mid valve (93-95 KX125/250 43mm forks do).
1997-2004 are 46mm KYB inverted cartridge forks with mid valves. slightly softer valving vs the otherwise virtually identical 96-97 KX125/250 motocross forks, as there was no longer an Open Class for the 500cc 2-strokes and the bikes were tuned more for aggressive recreational riding vs well groomed MX track racing. 96-97 KX125 stock springs are .38kg rate for those riders running the KX500 forks or triples, needing a lighter spring than the stock KX500 .40kg spring. 98 125/250 forks may be the same but there was one year with a different sized top clamping area on the tubes/triples, 98 or 99 perhaps. 98-99 KX125/250 all had progressive rate springs stock, which are frowned upon. KX500 had same straight rate springs all years of the 46mm inverted forks, 97-04. KX wheel swap or KDX custom machined axle spares are needed due to different axle diameters.

KDX250 1991-1994 triples are a direct bolt in, as are their inverted forks, but the valving is a little bit odd on these, look into this further for yourself. These triples will clamp onto certain years of KX forks however.
These forks all supposedly share the same upper and lower clamping diameters:
1991 - 1994 USA KDX250
1991 - 1995 KX125
1991 - 1995 KX250
1991 - 1996 KX500
(and I am assuming KLX300R as well, see below, triples could likely be the same or nearly identical to the 1990's KDX250)

KLX300R triples apparently will clamp directly to 1993-1995 KX125/KX250 forks to bolt directly into a KDX if using the KX front wheel. As with all other KX, YZ, etc Motorcross forks, they need revalved for woods riding in order to still get traction in the rougher sections. These are also taller, but bar risers / fat bar adapters will allow you to slide these up considerably in the KLX triples. Apparently I read that you can also use KLX330 (300? 230?) springs which are similar but shorter, and some spacers in the cartridge, to lower the fork internally.

Lastly, there are a few early years of KX125/250 triples which WILL bolt directly into the KDX frames, so the forks/triples and matching KX wheel will be a direct bolt on, but as with the rest, they will need internally lowered or else bar risers / fat bar adapters added to be able to slide the fork tubes up in the triples to lower back to stock KDX height and stock intended steering geometry.
1988 KX125/250 is a conventional cardtridge 43mm fork
1989 KX125/250 is a conventional cardtridge 46mm fork
1990 KX125/250 is an inverted/upside-down 41mm cardtridge fork
1991 KX125/250 is an inverted/upside-down 43mm cardtridge fork
the 125 came stock with .37kg springs all years 88-91. The 250 stock had .38kg and .39kg (91) springs those years).
89 and 91 would appear to be the years to have there. 46mm Conventional non-inverted cartridge forks sound really great for woods riding - although they have close to the same amount of underhang protrusion as the stock KDX forks, those '89 KX forks.
The KX500 I believe was the same as the 125/250 descriptions above as well.

On KX front wheels,
88-92 (& even earlier, basically all disc brake fork models) use a 17mm axle with 6203 bearings (17mm id x 40mm od x 12mm wide)
KX500 is the same but through 1993 also.
93+ KX125/250 & 1994+ KX500 use a 20mm axle with 6904 wheel bearings (20mm id x 37mm od x 9mm width). Some models as late as 2019 use this exact bearing part number https://www.partzilla.com/product/kawasaki/92045-1284
The KDX models use a 15mm axle with 6202 front wheel bearings (15mm x 35mm x 11mm)

Most other swaps of other KX forks will most likely require the KDX steering stem to be heated and pressed out of the KDX triple clamp and fit to the donor triple, as bearings are not available in the sizes needed. Other model forks will likely require the same, but I'm sure there are some that do have the required conversion bearing sizes available to make their triples a more direct fit.

Steering stops will likely have to be modified on many of these, but that is an easier detail to overcome, so I'm not looking into that part of the fitment.

KDXGarage wrote: 05:28 am Aug 10 2018
Unless there is something I am missing, then the following are just a direct bolt-in swap on bearings and triple clamps:

1986 - 2006 KDX200
1997 - 2005 KDX220R
1991 - 1994 KDX250
1993 - 1996 KLX250
1997 - 2007 KLX300R
1993 - 1996 KLX650
1986? - 1991 KX125 (could be earlier)
1986? - 1991 KX250 (could be earlier)
1986? - 2004 KX500 (could be earlier)

Somebody correct me if I am wrong. Also, be sure to check steering stop engagement.

1992 + KX125 / KX250 / KX250F/ KX450F / KLX450R all have the larger top bearing.

I don't know about KLX offset, but KDX250 triple clamp offset is the same as 1991 KX125 / 1991 KX250 / 1991 - 1993 KX500. 1992 - 1995 KX125 / KX250 / 1994 - 1996 KX500 is a little smaller offset.
Race Tech Gold Valve Install instructions:
https://racetech.com/page/title/IP%20FMGV%20POST%20TYPE

Rae Tech KYB / WP inverted forks - setting oil level:
https://racetech.com/page/title/IP%20Fk ... il%20Level

Cannon Racecraft springs pdf catalog for KYB, Showa etc forks:
https://www.cannonracecraft.com/wp-cont ... atalog.pdf
(note at the end it tells you the diameters x lengths of all their spring part numbers, so you can see that there are a few options for running shorter springs of the same diameter such as 41460 460mm vs 41470 470mm for these 96-97 KX125/250 97-04 KX500 forks to lower them 10mm internally with springs and spacers vs cutting the coils shorter which increases the rate also)

KYB 46mm Open Chamber disassembly video

Here's some KYB 46mm open chamber fork tips on disassembly, seal replacement, access to valving on both the base valve and the mid valve / rebound. This is the same basic fork as the 97-04 KX500, 96-98 or 99 KX125/250, and probably very similar to the 1995 mid valve 43mm KYB KX125/250 forks. Perhaps even the pre-mid-valve KYB open chamber forks as well.

https://www.thumpertalk.com/forums/topi ... bly-guide/
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
Jraldi
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Re: 97-04 KX500 / 96-97 KX125/250 swap - height & valving, vs KLX300R

Post by Jraldi »

FWIW I did the KLX fork swap and I love it. Night and day difference for me, If your over 180 with gear you might wanna do the .40 springs? I ride tame to gnarly trails. Bike performs and feels better in the woods now. Install was easy, you will have to modify the stops on T-tree, I just tapped and threaded a 10/32 stainless socket head to the existing stops and works perfect.

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KDXGarage
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Re: 97-04 KX500 / 96-97 KX125/250 swap - height & valving, vs KLX300R

Post by KDXGarage »

Very sharp KDX!
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
Jraldi
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Posts: 11
Joined: 07:43 pm May 13 2023
Country: United States

Re: 97-04 KX500 / 96-97 KX125/250 swap - height & valving, vs KLX300R

Post by Jraldi »

THX.. I absolutely love the last generation KDX. I recently threw on a 2014 KFX250F front fender to modernize it a little. After the fork swap, pipe & muffler, handle bars, new tires and sprocket change I shaved 10 pounds off the bastard and the 13/50 gearing is a game changer when I ride over in WV.

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