Starting a KX200 Hybrid

[gn83tm]

Well, I finally made the jump to upgrade the KDX a little. I picked up a 2003 KX125 and will install my 1990 KDX200 motor in it. I know a few guys have, and are doing, these hybrids but I don't recall hearing of anyone who has started with the '03-04 KX. Does anyone have any advice or know someone who has done this swap? Any pointers would be appreciated and I'll be sure to do the same for the next guy to try the project.

This bike will mainly be used for hare scrambles as well as some play riding. Does anyone have any good references for suspension work for this application?

Thanks!

 

[Duneman]

the 03-04 models are awesome, I put mine in a crf frame, but the 03-04 kx125 models will be awesome once it is done.
hang in there.

 

[gn83tm]

A CR chassis sounds like it would make a cool bike also.

I have both bikes stripped at this point and have made some initial measurements and started to lay things out. The DX cases where the swingarm mounts are 0.701" wider than the KX so I'll have to narrow things up there. If I recall correctly, that is about the same as with the earlier KXs. I think I'll try to machine the difference off of the swingarm instead of narrowing up the cases. It looks like the bearings sit in a ways so there's room to do that. I may need to recut the seal bore a corresponding amount. The swingarm bolt is also larger so I'll have to bore the cases accordingly.

The front engine mounts seem to be close to the right height but about 1/2" too far forward. The width there is the same between the 2 bikes. The lower mounts were too narrow to start with so I cut them off to see where I needed to be. I think they would have been close front-to-rear and in height. I might have been able to bend them out to allow the motor to drop in.

The stock KX tank fits well and clears the water outlet and rear head mount fine. The DX motor is 3 lbs heavier than the KX. Not bad for 75cc more. Half of that is probably the heavy DX kicker and the rest is maybe in the flywheel.

The KX pipe (I have a PC) has major interference with the KIPS cover and it actually slides over the outlet on the cylinder instead of inside it so there's no chance of it working. I think I'll look for a later model DX pipe to see if that is closer to start with. Does anyone have a stocker they want to part with for a small fee? If I get one and it looks doable I'll order a FMF or PC at that point and try to get it to work.

I'll keep posting as to how it's going. Unfortunately I have to work all weekend so there won't be any progress for a few days.

At the GNCC race in Texas I noticed the KXs that Steve Hatch and others are running for Team Green. The Throttlehead.com graphics they are using look pretty cool. Does anyone know where to get them?

 

[Duneman]

I had the same problem, I have a 93 engine and used a 97 Pro Circuit pipe, I cut that piece out of the pipe and reversed it so it dished in and welded it back and BAM! it fit.
What would it look like if the DX swingarm was on the KX frame or will it fit. A 91 KX125 kickstarter will fit all KDX's and the are aluminum, that's what mine has. Keep me informed, it's educational. thanks.............

 

[BucKat]

My conversion in progress.
The host provider is a bit stuborn so keep refreshing until the pages come up.
I have published upto step 5.
http://mywebpage.netscape.com/Buckatana12/home.html


The KDX swing arm will fit directly on the KX frame but to what advantage would that be. Makes the bike look weak in the rear.
I too opt'd to cut the swing arm instead of machining the engine. I've detailed this process with pictures and technical drawings on my web page. My measuring tools are in metric but you'll get the idea.


DYNOPORT makes custom pipes just for this project. I'm told the power delivery is similar to a FMF Fatty but with a wider power band.

E-mail me with any questions and I'd be glad to help where I can.

Cheers.

 

[placelast]

I bought the second-to-the-last Dynoport KDX/KX pipe; you might want to snatch up the last one. It's raw metal but worth it.

Suprisingly, I did not feel any difference in the power delivery between the new pipe and the previous custom-fabbed FMF. The FMF had a slightly flattened headpipe when I bought it, so maybe that's why but I expected the DP to have huge bottom gain. Don't get me wrong; I still like it (good looks). It had a huge chamber and sticks out begging to be smashed, but is made of thicker material vs. other brands and has held up well to crashing.

BTW: my hybrid is a '90 KDX engine in a '98 KX125 chassis, with '97 RMX front end. Modifications are too much to list here.

 

[gn83tm]

Well, the job I was working on this weekend got shortened so I got back into town this evening and was able to spend some time in the shop working on the project.

I machined the swingarm sleeves down so I'm at the proper width there. It sounds like the '03/04 KX sleeves must be the same width as the earlier bikes. I took off 0.351". I drilled the cases out but need to grab the right size reamer from work to bring that bore to final size.

With the engine mocked up in the chassis, things seem to fit pretty well so far. The front mounts need to be replaced with some that move the hole back about 1/2". I think I'll wait to do the mounts until I come up with a pipe in case I am able to move the engine slightly to help the pipe situation. Does anyone know if the Dynoport pipe will fit the 03/04 chassis? I guess they'll be my first call Monday morning.

The carb situation looks like it may take a little work. The PWK is good on length but sits high in the air box boot and is smaller in diameter. I could probably machine a spacer to clamp onto the back of the carb but doing the vertical offset and making it flare out into the boot so there isn't a sharp step will get a little complicated. The other option would be to maybe use the new high-tech Mikuni from the KX. The outlet is larger but it will go into the reed cage boot. It is a 38mm carb but has a fancy slide setup to help give the KX some low end. It was bragged up quite a bit in the KX reviews but who knows what kind of a bag of worms I'll open up if I try to use it. Does anyone know any carb experts who may be able to provide some insight into this?

The tank fits with pleanty of clearance so that's one issue I won't have to deal with. At least until I find out it's not big enough to run a 2 hour race and the oversized, aftermarket tanks won't fit. The tank and head stay layout was one of the main reasons I went with the 03/04 model and I'm glad I did.

Thanks for all the help guys! I probably won't have a nice website devoted to this project but I am taking a lot of notes and pictures to help out anyone else in the future. So far I haven't heard of anyone using the 03/04 KX for one of these projects. I hope it goes relatively quickly since I'm ready to go racing. My buddy's going to the race at the John Zink ranch (site of the ISDE 10 yrs ago) in a few weeks but I don't think I'll make that happen.

 

[Duneman]

Well on an an 01KDX the swingarm is to no advantage if I remember right, but with the 89-94 they have they quick change rear wheel, and the can be pollished up and look fine. The 94-98 kx125 chassis are great and so are the 03-04 kx125s. I would not do it in the 99-02's. I have ridden all 3 conversions. Theres no reason why the 95-97 DX pipe wouldn't work. It might have to be extended right where it hooks up to the cylinder, but other wise that's it. And if you have a gas welder or a small mig wire welder they both work great, heck buy a stock one off ebay and use that and if you succeed than try it on yours. Gas welders are cheap and so are the tanks. I posted a pick of mine on here before, if you have not seen it check it out. Here is what my bike will look like when it's done. I'm almost there.

http://www.angelfire.com/ultra/mkr/

 

[farmerj]

Duneman,

What kind of paint did you find to fancy up those plastics? Did it really stick?

Jeff

 

[Duneman]

Duneman,

What kind of paint did you find to fancy up those plastics? Did it really stick?

Jeff

My bike will actually have a green tank and the rear fender will be black, the pic posted is just art work to get an idea of what i wanted to accomplish, on the link is a pic of my bike and none of the bike is painted.

 

[BucKat]

I would not do it in the 99-02's.

Why not??

 

[Duneman]

They where gurthy,not the best turners, and had little padding on the seats, not what you want for a woods bike. The 94-98's had nice padding on the seats and the gurth was much lower, the 99-02's felt big as far as 125 standerds go. The 94-98's where a smother ride with the seat tank junction. If you can find a nice 98 sit on it and then site on a 99. In the 99-02 125 shoot outs they eather came in last or tied for last, and it wasn't always cause it suffered from a slow engine. Hell just look at the differences, in looks alone. I just went through my pile of DirtRider ,MotoCrossAction, and Dirtbike mags. :think: The 03 chassis and 04's are awesome.

 

[placelast]

The KDX engine is taller than the KX125, and so is the location of intake from the carb. As a consequence it is snug and alignment is not quite right in the air boot side but close enough.

On the upstream side of the carb the prev. owner fab'd an off-center ring; the ring's outer diameter matches the KX boot, while the inner matches and mates to the KDX PWK carb. The offset is towards the outboard side to clear the shock spring.

 

[gn83tm]

I called DynoPort today and asked about a pipe for this conversion. They said they haven't done any work with '03/04 KX chassis so didn't really know how their conversion pipe would fit. They didn't have one in stock but could make one up in a week or two if someone wanted one. They're going to send me the cones and other parts and I'll build my own pipe from pretty much scratch. Not a big deal since I've done a lot of this type of work for a living (on the race car side) but it definately will take a few hours to get done. They're also sending a spark arrestor with some loose brackets so I'll get to build that also.

I'm still mulling over which carb to use. Does anyone have any insight or know of someone who might?

As far as using the DX swingarm goes, I'd be real hesitant to do that. Who knows what suspension geometry you'll end up with doing that even if all the pieces bolted up.

The fun continues!

 

[placelast]

I'm still mulling over which carb to use. Does anyone have any insight or know of someone who might?

The fun continues!

I'm afraid to say the fun won't be over for a looooooooong time.

I'd suggest using a stock carb as the bigger KX carb would be too much throat - intended for high RPM (MX) running; the KDX is better suited for trial/enduro use and not WFO. A Keihin 36mm PWK is stock.

That's a good deal they would do it or send you the pipe parts, so long as they told you the order of the cones!

 

[BucKat]

They where gurthy,not the best turners, and had little padding on the seats, not what you want for a woods bike. The 94-98's had nice padding on the seats and the gurth was much lower, the 99-02's felt big as far as 125 standerds go. The 94-98's where a smother ride with the seat tank junction. If you can find a nice 98 sit on it and then site on a 99. In the 99-02 125 shoot outs they eather came in last or tied for last, and it wasn't always cause it suffered from a slow engine. Hell just look at the differences, in looks alone. I just went through my pile of DirtRider ,MotoCrossAction, and Dirtbike mags. :think: The 03 chassis and 04's are awesome.

Understood....Thanks for the insight.
However........I will continue using my '00 chassis as that is what I have.
At any rate...I've never riden anything other year than a '96 and most likely never will have a chance to ride any other . This is good for me as I'll have nothing to compare to...


P.S.

The air box snorkle from a 94 KX125 will fit the KDX carb. Something to consider.



Joe