Originally Posted by b1dude

My question for you, now that you've had a KX apart right next to a KDX....what are the biggest differences besides gas tank size between the two setups. One of the biggest critiques of our KDX's by the magazines is that the KDX is heavy compared to the competition (KTM 200, etc.). What major components (frame, swingarm, etc.)are the biggest offenders of the "overweight" sin?

I've started wondering what I could do to my USD forked KDX to put it on a "diet" and bring it's weight down to something similiar to you hybrid. Curious what your experience with your hybrid would point to for areas to target for weight reduction.

Originally Posted by arjay

First off I've got to say what great jobs you guys have done. I've been thinking about this for a long time, and this thread has really got me going.

I have a slightly different proposition and would like to get your thoughts on it.

I've got a fully rebuilt aircooled 87 KDX200 motor ready to go. Rather than put it into the unrestored original boneshaker chassis, I want to find a new home for it. I love the idea of a lowtech woods bike with sharp handling and trick suspension. Having no rads and water could make it a sub 200 lb contender. The engine would be ported for a harder hit.

The natural option (in frame heritage) would be an 86 KX125 with rear disc and linkage suspension. The single down tube fits the side exhaust port. Drawbacks would be that this was a first stab at the format for Kawasaki and only got better from there in. Also it's quite raked out compared to later geometry. 27.5% compared to the contemporary mx'ers, 23 - 25%) The back end could be updated with an 89/90/91 swingarm and linkage.

A guy at the local bike shop has a 94 perimeter chassis. This seems a bit more like it. A bit more work though. It would mean losing the twin cradle and welding in a square section down tube, continuing from where the original one stops. Other issues would be building a pipe for the side port exhaust that goes around the cylinder fins without sticking out too much. I guess the fins could be ground back to accomodate it.

Thanks for any thoughts.

ps has anyone tried running an aircooled 200 motor with modded digital ignition from an 03 onwards KX125? Vortex do a reprogrammable unit for the 125. Maybe mapping could be adapted to suit the 200.

Originally Posted by arjay

Hi Mark, other aircooled motors that I was thinking about for a 125 chassis were RM250, RM400, PE400, KX250 (all 80/81 vintage - so spares and robustness could be a problem) The RM400 is a great engine, smooth and loads of low end. Just doesn't have primary kickstart. I like the sound of the quad route, newer engines would be better.

Have you got any pics of the WR200?

Originally Posted by arjay

Mark, that's a beauty. Why didn't Yam build it in the first place?

How tricky was it compared to the KX/KDX?

The DT200 gearbox would go straight into a new Blaster 200 motor, as the cases are the same. The standard cylinders can be ported for 30bhp, and there's a 240 kit that gives 40+. There are heaps of aftermarket tuning parts.

http://www.trengaracing.com/catalog/blaster.php

The cases look kind of dated though, like a DT175. No powervalve, but I guess that keeps things simpler.

Originally Posted by Rog

I had an 89 kx125 with an air cooled kdx200 motor about 4 years ago. Wish I had never sold it. I' v just come across a complete rolling kx125 frame and was thinking I could make another one. I never really took much notice of my old one but was wondering how easy the motor slotted in and were there any major mods to do to get it to fit. The old one just looked like it was made like that from the factory. Do any of you guys know?

Originally Posted by arjay

Hey Rog, could you email me. I'd like to get some advice from you on the down tube set-up.

Thanks

- Nice job Kev. What forks are those?

Originally Posted by GS

What year(s) of KX chassis would be prefered for the conversion??
Have a 03 KX125...love the handling and a '99 KDX220 of which I love the power delivery. Won't use these two, but what generation of KX makes sense?? I can "ebubbl bait an engine , me-guesses
Greg

Originally Posted by mark_england

, id use a current kx125 frame and a post 95 kdx200 engine which i'd bore to 225cc

Originally Posted by arjay

why the 200 motor not the 220?

Originally Posted by ebeck

I have seen that done.

Originally Posted by m0rie

Bringing this back to the top. Mark when you used the GasGas200 pipe did you have to do any modifications to the head of the pipe where it meets the cylinder? If so do you have any pictures of it and any pictures of the head stay that you made?