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

[KDXGarage]

You may be able to just run a 1989 - 1994 KDX200 wheel in the 1986 - 1988 KDX200 if you make the various brackets and holders, plus modify the swingarm hub holder to mount the disc caliper. A 3mm washer on one side seemed to line it up for me many years ago in a test mount.

[Chuck78]

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

I have too many projects going on right now, and have come to the realization of that again as well as the wife's potential to murder me or divorce me if I bring home any more projects without finishing a few and selling them which I've lost interest in (Suzuki GS vintage street bikes & 1 of 2 vintage Suzuki PE's)... so this pipe dream is on hold for a while, but with luck, I might be able to shop around this summer and potentially start working on one of the above the following winter...

The idea of any of those three combinations above sounds quite appealing, so this is a pipe dream project that will be on my mind for quite a while. Being able to run a tighter piston to wall clearance on a water-cooled 134 cc engine is definitely a bonus, so really all three of those possibilities are of great interest to me. I hardly ride my street bikes anymore so I will try and pair that down to 3 bikes total or even 2 projects & 1 running street bike in order to justify some more dirt machines!

Does anyone want to buy a vintage '76 Rickman CR road racer project chassis with a GS1000 engine? A '78 Suzuki GS1000 8V project? A Suzuki GS750 8V runner!?!?
Or an '83 Suzuki PE175 Full Floater 2-stroke enduro bike?!?

[KDXGarage]

I am not a marriage counselor by trade, but I heard it is better to ask for forgiveness than permission.

[Chuck78]

Previously I'd snatched up a pair of '94-'98 KX purple shrouds, in anticipation of acquiring a '95-'98 KX125 for a 134cc woods bike project...
So I effectively bought a pair of shrouds to build a bike around

Well... Now I've been picking up some other '94-'98 KX125/250 parts, an Acerbis oversized purple desert tank and a '94-'98 Acerbis 035 spark arrestor, + an AC Racing aluminum seat subframe (stock '94-'98 was a thin steel subframe).

However, I believe I've decided for now that I may be using those KX parts to put my spare KDX220 engine into a new home... building a KDX220/KX125 hybrid... I have yet to acquire a frame/swingarm or other parts, so I still may end up with finding a blown up '95-'98 KX125 complete, which could revert back to this KX134X / KDX134R ultralight woods bike conversion, but I may go the hybrid route for now...
Frames on eBay are cheap enough that if I changed my mind after modifying the 125 frame to KDX200/220 engine mounts, I could always pick up another '95-'98 KX125 frame and do this exact proposed build still or even swap all the parts onto the stock KX125 frame and woods built 134cc engine.


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Thinking about how much I fall back on using the lugability of the torquey KDX220 engine, and how well the 200H/220R engines can be modified, as well as the allure of the removable seat subframe, slightly higher ground clearance, and slightly lower fuel tank height, as well as being by default (longer shock stock than the KDX) a better candidate for a longer modern shock swap (similar size shock in a KDX requires some mixing and matching of parts to keep it no more than 12mm taller than stock) as well as defaulting to fitting taller forks to match the taller rear suspension, I decided a 220/KX125 hybrid would be a fun route to try.





Upon acquiring these KX parts, I was also contemplating the opposite direction, finding a 1997 KX250 to do a woods conversion on, possibly a +2.10mm overbore Wossner/Vintco piston for 265cc to get a little more edge for running more even in the wide open & hill climbs up against modern 300's... some porting cleanup and blueprinting/gasket matching, RAD valve reed cage, thinner base gasket to very slightly drop the port timing, and head squish mods for a little more low end torque, + flywheel weight, 18" wheel, woods valving etc... Oh, and a '91-'94 KDX250 wide ratio gearbox swap...




Ultimately I decided that the KDX220 or a big bore 223cc KDX200 engine with revised porting is plenty enough power for most riding scenarios up to 55mph, & the 250cc & larger engines definitely have more weight to them, & I'm trying to drop weight through these builds... So for now, that idea is just a brainstormed pipe dream... Additionally, the KX250 frames are a bit longer in the front end as well as I believe(?) a slightly longer swing arm, I do really love the small bores for their nimble agile handling abilities due to a slightly more compact chassis...

[Chuck78]

Was skimming through this... and you make some good points.

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

I thought that sounded a little off, so I looked up the 03-05 KX frames, as I don't recall them ever being a wishbone style like the majority of modern KTM frames, the very dated 1988-2004 KX500, '89 & earlier KX250/125, & '94 & earlier KDX200/250 etc...

Looking up some eBay frames, the 03-05 KX 125/250 frames are basically just like the 95-02 KX125/250 perimeter frames aside from a different geometry, they're a little bit lower with less ground clearance and a lazier steering angle but similar wheelbase. Much thinner seat, and narrower frame and seat, but still a perimeter frame. So you probably save maybe 1.2 lbs up top perhaps from the even thinner seat and the slightly narrower frame, but it's not too much of a difference other than ride height is a bit lower. Personally I will take an extra 1.5 lbs in a much more comfortable seat for all day rides... He can't be standing up the entire time for 7 or 9 hours!

The '99-'02/'03-'05 forks are considerably lighter than the '96-'98 forks, however... Those very well loved open chamber 46mm KYB forks used 96-98 were quite heavy.