89 KDX / KX hybrid for vintage MX?

Discussion for swapping a KDX motor in a MX frame...
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Berniepiet
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89 KDX / KX hybrid for vintage MX?

Post by Berniepiet »

Hi guys, I am new to KDX's. I race vintage MX and we have a class for 89 and older 0-200 cc's. I have an 89 KX 125 and saw a CL for an 89 KDX 200. Can the combination of these two be made into a great vintage motocrosser.

I have a KTM 200SX that I love for modern MX. I love to humiliate the 450's on it. Would like to try the "200 Soultion" in vintage. I could have Eric Gore build the motor as an option. I don't think I want to get into stuffing the 200 engine into the 125, so I will stick with the 200 frame.

Can the engine be made MX fast, ie more hp, less torque , use the 125 transmission etc. or is this just an excercise in frivolity? Is the older tubular frame ok for MX use?

Thanks for your input
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Re: 89 KDX / KX hybrid for vintage MX?

Post by 6 Riders »

I raced my 93 KDX in a Vintage class this summer....Now, I SUCK at track riding, but I couldn't pass up racing (my first race) on a Nationals track, so I did it. IMO the motor is plenty powerful enough for MX, it will eat 125s given proper gearing. The part of the bike that lacks is the frame geometry. The short rake of the KDX forks makes it a little hard landing for MX. But if you can keep the jumps "low and straight" (which I, in fact, can not do) then the KDX would be fine. I would use the KX frame and cram that 200 motor into it. It might be easier than you think. The KDX frame is based off the previous generation KX, so going into an 89 frame should be pretty simple. If you choose not to go that route, you'll want the forks off of the KX, built and shortened for the KDX and maybe the 19" rear wheel.
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Re: 89 KDX / KX hybrid for vintage MX?

Post by newbbewb »

I have a 89 hybrid. Can it race? Absolutely. The suspension is great! With a 200 it frickin rips. The kx125 in 89 had the best suspension of the japanese bikes hands down.

There really is very little work the fit the E series kdx engine in the 89 kx125. I have no BS issues with anything at all. Aside from the engine mounts and swingarm mod, it's a plug and play. I highly recommend it, you won't be sorry.

The only reason to NOT use the kx, specifically the 89 with the wonderful suspension, is because in 91 kawi went to perimeter frame, had 2 radiators, and visually looked better. In my opinion a newer kx would be a better choice. With that being said, my 89 never overheats, the frame feels pretty darn good, and I'm not looking at it when I'm on it. Smiles every time.

The E series kdx 200 engine responds to bolt on mods very well, but leave it at that. A MX engine it is not, don't bother. The good news is that It's a 6 speed, and with said bolt on's it's got a really nice mid-range hit. Also of mention is how much abuse they will take, and like it.

In a drag race, a 2004 yz250 in great shape with pipe and good rider, vs my hybrid with bolts ons is dead even, until the yz runs out of gear. :butthead:
93 kdx200-Highly modified
89 kx125/kdx200E engine
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89 KDX / KX hybrid for vintage MX?

Post by KDXGarage »

Berniepiet wrote:Hi guys, I am new to KDX's. I race vintage MX and we have a class for 89 and older 0-200 cc's. I have an 89 KX 125 and saw a CL for an 89 KDX 200. Can the combination of these two be made into a great vintage motocrosser.

I have a KTM 200SX that I love for modern MX. I love to humiliate the 450's on it. Would like to try the "200 Soultion" in vintage. I could have Eric Gore build the motor as an option. I don't think I want to get into stuffing the 200 engine into the 125, so I will stick with the 200 frame.

Can the engine be made MX fast, ie more hp, less torque , use the 125 transmission etc. or is this just an excercise in frivolity? Is the older tubular frame ok for MX use?

Thanks for your input
Sooo, you are not wanting to put the KDX engine into the KX frame, just KX parts into the KDX engine?? I don't think that will work.

I would much rather race a 1989 KX125 in MX than a 1989 KDX200. If it were a woods ride or race, would prefer the KDX. Select the correct tool for the job.

See if Eric Gorr can make the 1989 KX125 into a 133 or 144 or other big bore.
Thank you for participating on kdxrider.net. :bravo:
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89 KDX / KX hybrid for vintage MX?

Post by vintagekawi »

Hi Bernie, I had the same question as you. I had a blown up 89 kx 125 parts bike and 89 kdx that ran but was totally used up. wound up putting the two together and made one bike out of it. The frames on both bikes are very similar. rear suspesion is a direct swap, and forks are a straight swap. Originally i wanted to just bolt the kdx engine into the kx frame, but it didnt really fit that great and required some cutting and welding of the lower tubes and mounts, I also wasn't sure if it would overheat with one radiator. So I then decided i would use the kdx frame and put all the kx suspension in the kdx frame, with 46mm kayabas up front. The KDX has 1/2 degree steeper steering angle, I think it corners better than the 89 kx also. I really enjoy riding , and racing it in the vintage class. it is very competative with the 125's of the era, and really surprises alot modern riders at the practice track when they get passed by 25 year old trail bike. I can turn faster lap times on the hybrid than i did on my 89 kx 125. Its also much easier to ride due to the characteristics of the engine. Good luck keep us posted if you go ahead with the project.
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Re: 89 KDX / KX hybrid for vintage MX?

Post by masterblaster »

I've ridden the e series and the h series around the track with stock suspension with similar results...absolutely terrifying past third gear...I don't know if your class allows you to run a newer fork but that's what I'm in the process of. At speed the kdx is the wrong tool for the job however on a tight track the kdx will destroy a 125 I was clearing big transitions right out the corner that I cannot connect with my brothers 01rm125! Any who if it's a fast track the kdx would be ill advised as it is a twitchy beast without a lot of work.
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Re: 89 KDX / KX hybrid for vintage MX?

Post by masterblaster »

One more thing...if it's deep dirt in the corners you will be a full gear higher on the kdx the grunt allowed me to hit the fluff on the outside without losing all momentum like on the rm
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