KDX Conversion

[Ignitus]

Ever since I saw this discussion:

https://www.vitalmx.com/forums/Race-Sho ... me,1267741

I've wanted to do something similar. My dream bike would be to take a 220r (various power mods bringing it about equal to a base 300. my brother's almost has more kick than my 2013 300 xc-w) engine, and stick it in steel kx frame. Add some of the luxury pieces like a hydraulic clutch lever, inverted forks, direct injection, and mapping. Also other random things such as a ktm headlight/shroud, street legal kit, modern plastics, and more. Basically make the ultimate kdx (wannabe 300) that so many of us wish existed today.

So has anyone seen or made a modern Frankenstein bike like I described above? Guys who are big into project bikes. Any advice for a youngster with low knowledge? What do y'all think would make the perfect kdx? I see this being a decade+ length project because I'm about to start college. Soooo, any tips about making progress during college?

[Tyl3r]

See the KDX-MX hybrid section of this forum: KDX-MX Hybrid

Quite a few nice ones in there with tons of info how it can be done. Unfortunately, the 125's are going for a lot more than they were a few years ago. You can spend however much you want on it. When I built mine, I got to a point where I ran out of money, so I just got it rideable. Then Just slowly kept updating it from there, making it exactly how I wanted it. Here's a photo:

20220406_194133.jpg (1022.69 KiB) Viewed 1408 times

[Ignitus]

Man that is a gorgeous looking bike. Thanks for the tip off, never seen that section before.

[bufftester]

Like Tyler said, check out the hybrid section of the forum. Lots of really nice ones have been done. I have about 10 years on mine now and love it just as much as I did in the beginning.

[SS109]

Yep, in the hybrid section there have been numerous conversions done on multiple brands of chassis. I know I'm planning one on an '06 KX250F chassis which is one of the aluminum frames. Once I get my GasGas done I'll start really planning for it.

[MoonStomper]

So as usual I’m late to the party here… why are folks putting KDX motors in non-KDX chassis? What’s special about the KDX motor versus the KX? I get that the trail/dual sport chassis design of the KDX is heavier and maybe not as aggressive as the KX chassis, but why not just ride a KX in the woods with a few woods mods if you want the lighter/more aggressive frame?

Please educate me, thanks.

[smelonas]

So as usual I’m late to the party here… why are folks putting KDX motors in non-KDX chassis? What’s special about the KDX motor versus the KX? I get that the trail/dual sport chassis design of the KDX is heavier and maybe not as aggressive as the KX chassis, but why not just ride a KX in the woods with a few woods mods if you want the lighter/more aggressive frame?

Please educate me, thanks.

The wide ratio transmission is a big ticket item. 5 speeds is not enough for people that ride anywhere but a track. The stock motor is a good candidate for upgrading. Between a carb, new CDI, reeds and a few other tasty mods, the thing can actually rip. Plus, the suspension of the MX bikes is leaps and bounds better. Consider also that changing forks on a KX frame to KXF forks is much easier as well. Or if you are lucky, some SSS forks. Plus the KDX is a true pig on the scale. I am not sure what they weigh, but they are frikin heavy. Lot of reasons really. Kawasaki never made an 'X' model 2 stroke that was up to date for the time. The H series KDX was a cheap, but capable and fun off road 2 stroke that missed a couple of marks, but could be heavily modded to be a weapon or be swapped into a better frame.

Thats why.

[SS109]

KX's are good chassis wise but their engine/transmissions really leave something to be desired. No wide ratio, only 5 gears, MX engine tune, lightweight flywheels, no lighting coil (you can run lights on the newer e-start models), and in the case of anything made after '07, 4T's are just more costly to rebuild and harder to service/repair.

For the record, I weighed my KDX in at 242lbs with 1 gallon of fuel, aluminum skid plate, wraparound bark busters, heavy Maxxis SI/IT tires with the rear being a 120/100-18, and 47mm Showa USD forks. So, add an additional 13lbs for the 2.2 gallons to fill it would be a total of 255lbs roughly. The DirtBikeChannel has weights listed for the bikes he has tested, all with full tanks and no aftermarket parts, and the KDX isn't that horrible when you compare it to most modern true off road/enduro bikes. He has the 2023 KTM 300XC at 239, '22 GasGas EC300 at 246.5, and a '20 Sherco 300SEF at 253.5 plus many more on there. Check out the weights here: https://dirtbikechannel.com/pages/bike-weight

Now, that all said, the reason I want to do one is that I absolutely love the way my 220 lugs and pulls and is rock solid reliable and I don't want to give it up, the KX250F chassis will be more stable in the whoops which are a common thing here in the dez, I'll hopefully get a little weight savings, it will be cheaper and easier to find plastics and other chassis parts, and my '98 KDX220 chassis has about 1200 hours on it since I rebuilt the engine and no clue how many before I bought it in 2015, and I've already had to weld it up twice due to mounts that have broken.

[MoonStomper]

Well there you go! Thanks for the briefing y’all, makes a lot of sense.

[smelonas]

KX's are good chassis wise but their engine/transmissions really leave something to be desired. No wide ratio, only 5 gears, MX engine tune, lightweight flywheels, no lighting coil (you can run lights on the newer e-start models), and in the case of anything made after '07, 4T's are just more costly to rebuild and harder to service/repair.

For the record, I weighed my KDX in at 242lbs with 1 gallon of fuel, aluminum skid plate, wraparound bark busters, heavy Maxxis SI/IT tires with the rear being a 120/100-18, and 47mm Showa USD forks. So, add an additional 13lbs for the 2.2 gallons to fill it would be a total of 255lbs roughly. The DirtBikeChannel has weights listed for the bikes he has tested, all with full tanks and no aftermarket parts, and the KDX isn't that horrible when you compare it to most modern true off road/enduro bikes. He has the 2023 KTM 300XC at 239, '22 GasGas EC300 at 246.5, and a '20 Sherco 300SEF at 253.5 plus many more on there. Check out the weights here: https://dirtbikechannel.com/pages/bike-weight

Now, that all said, the reason I want to do one is that I absolutely love the way my 220 lugs and pulls and is rock solid reliable and I don't want to give it up, the KX250F chassis will be more stable in the whoops which are a common thing here in the dez, I'll hopefully get a little weight savings, it will be cheaper and easier to find plastics and other chassis parts, and my '98 KDX220 chassis has about 1200 hours on it since I rebuilt the engine and no clue how many before I bought it in 2015, and I've already had to weld it up twice due to mounts that have broken.

Thanks for taking that weight! I have stock toolbag, kickstand and handguards intact, but a BD headlight, same 47MM 125 forks, so my bikes weight is close to the same. The KDX doesnt wear the weight well, I will say that.

When I lived in Vegas, I found the KDX quite good in mid to high speed off road. Not as good as my 07 KXF, which must have been made for that exact application, but it held its own. Once the 47mm forks were on and the shock was done by fredette, thing was a bullet on mid speed stuff. Very efficient. I have never cared for the way our hybrid turned out. I think next time I am in Vegas I am going to shove the forks all the way to the bars. Nice light bike, but it doesnt feel nearly as light as my 07 CR125. That hybrid just needs a lot of help, it never got 'dialed'. I am afraid it will be too good once I get it right!!

[Tyl3r]

I have never cared for the way our hybrid turned out. I think next time I am in Vegas I am going to shove the forks all the way to the bars. Nice light bike, but it doesnt feel nearly as light as my 07 CR125. That hybrid just needs a lot of help, it never got 'dialed'. I am afraid it will be too good once I get it right!!

What chassis did you use for your hybrid? I am sorry to hear that it didn't turn out so well for you. For a while, I had a stock KDX and and my hybrid. Riding them back to back was like night and day. Relative to each other, the KDX was tall and heavy and turned slow and the hybrid was like riding a mountain bike. It just felt better balanced, like it could turn faster, and was less top heavy. To me, it took a bike that I thought was fun to ride (the KDX) and turned it into a bike that I absolutely love and don't really ever want to replace, even with it being kickstart only lol.

[smelonas]

I have never cared for the way our hybrid turned out. I think next time I am in Vegas I am going to shove the forks all the way to the bars. Nice light bike, but it doesnt feel nearly as light as my 07 CR125. That hybrid just needs a lot of help, it never got 'dialed'. I am afraid it will be too good once I get it right!!

What chassis did you use for your hybrid? I am sorry to hear that it didn't turn out so well for you. For a while, I had a stock KDX and and my hybrid. Riding them back to back was like night and day. Relative to each other, the KDX was tall and heavy and turned slow and the hybrid was like riding a mountain bike. It just felt better balanced, like it could turn faster, and was less top heavy. To me, it took a bike that I thought was fun to ride (the KDX) and turned it into a bike that I absolutely love and don't really ever want to replace, even with it being kickstart only lol.

We used the one off 2003 frame, which ended up being the luckiest thing ever because I was easily able to make some custom length lowering links for it that were no longer made by PC. We swapped on some showa twin chamber KXF forks, which have always been harsh and non compliant. The shock not being much better, but good enough usually. The motor has also always been a rich, and simultaneously lean pig. Its got the port job and head mods and I wasted 500 bucks having the carburetor worked over. Bike has always seemed hesitant to turn as if the front end is way too high. Its stable in a straight line, hence my comment to shove the forks to the bars and it doesnt have that light flickability that my CR has, but to be fair, honda had that third gen AL frame dialed. Buying that CR has probably been the worst purchase I have made as it has ruined my taste in how bikes should handle and feel.

But I have a plan to buy an Ohlins shock, I have a number of jets and needles to try and get it running perfect, and a laundry list of other things (headlight/stator, lots of cerakote and vapor honing, a used but untouched 220 cylinder, build a new wiring harness, etc..) Really going to finish that bike up and make it sweet. Its just literally a thousand miles away, so it will probably take an actual decade to do it all.

I finally got my KDX dialed and it is a blast to ride. I really have enjoyed the work it has taken to get that bike to where it is and how much I have learned along the way, a good bit in part to this forum. From the suspension to the jetting, I have learned a lot and am really getting into the good stuff now!

[SS109]

Thanks for taking that weight! I have stock toolbag, kickstand and handguards intact, but a BD headlight, same 47MM 125 forks, so my bikes weight is close to the same. The KDX doesnt wear the weight well, I will say that.

When I lived in Vegas, I found the KDX quite good in mid to high speed off road. Not as good as my 07 KXF, which must have been made for that exact application, but it held its own. Once the 47mm forks were on and the shock was done by fredette, thing was a bullet on mid speed stuff. Very efficient. I have never cared for the way our hybrid turned out. I think next time I am in Vegas I am going to shove the forks all the way to the bars. Nice light bike, but it doesnt feel nearly as light as my 07 CR125. That hybrid just needs a lot of help, it never got 'dialed'. I am afraid it will be too good once I get it right!!

Yes, the KDX does not wear it's weight well at all. My KDX performs great everywhere except the high speed stuff (45+mph) where it feels twitchy and not connected to the ground. Guys can blow by me in high speed sand sections like I'm sitting still because I'm having to really concentrate on keeping the KDX going where I want it to. I assume this has to do with the KDX chassis being a short wheelbase bike vs what most modern bikes are. The fork and shock upgrades helped this a lot, IMO, but can't fix wheelbase.

Once you get that hybrid dialed in I'm sure you love it as much, if not more than, as a fully upgraded KDX chassis. On your '03 chassis, make sure you have 22mm offset triple clamps. They came stock with 25mm offset which just doesn't work on that chassis. It will feel like it wants to push in the corners yet at the same time knife under you. The forks and shock can both be made to be super compliant. Find a good suspension shop and get it done and make sure you have the correct springs. Also, lowering the bike with links will mess up the chassis' geometry. Either run the stock links and live with the height or have the suspension tech lower the forks and shock internally to get the best handling out of any bike. Trust me, even an Ohlins shock won't work as well as you expect with lowering links.

[smelonas]

Thanks for taking that weight! I have stock toolbag, kickstand and handguards intact, but a BD headlight, same 47MM 125 forks, so my bikes weight is close to the same. The KDX doesnt wear the weight well, I will say that.

When I lived in Vegas, I found the KDX quite good in mid to high speed off road. Not as good as my 07 KXF, which must have been made for that exact application, but it held its own. Once the 47mm forks were on and the shock was done by fredette, thing was a bullet on mid speed stuff. Very efficient. I have never cared for the way our hybrid turned out. I think next time I am in Vegas I am going to shove the forks all the way to the bars. Nice light bike, but it doesnt feel nearly as light as my 07 CR125. That hybrid just needs a lot of help, it never got 'dialed'. I am afraid it will be too good once I get it right!!

Yes, the KDX does not wear it's weight well at all. My KDX performs great everywhere except the high speed stuff (45+mph) where it feels twitchy and not connected to the ground. Guys can blow by me in high speed sand sections like I'm sitting still because I'm having to really concentrate on keeping the KDX going where I want it to. I assume this has to do with the KDX chassis being a short wheelbase bike vs what most modern bikes are. The fork and shock upgrades helped this a lot, IMO, but can't fix wheelbase.

Once you get that hybrid dialed in I'm sure you love it as much, if not more than, as a fully upgraded KDX chassis. On your '03 chassis, make sure you have 22mm offset triple clamps. They came stock with 25mm offset which just doesn't work on that chassis. It will feel like it wants to push in the corners yet at the same time knife under you. The forks and shock can both be made to be super compliant. Find a good suspension shop and get it done and make sure you have the correct springs. Also, lowering the bike with links will mess up the chassis' geometry. Either run the stock links and live with the height or have the suspension tech lower the forks and shock internally to get the best handling out of any bike. Trust me, even an Ohlins shock won't work as well as you expect with lowering links.

I built the lowering links to 125mm(ironic on a 125 frame), which was 1.5mm longer than stock, same length that pro circuit made them. The links really settled the rear down a lot and made it much more friendly, so I will more than likely leave those. The lack of a high speed adjuster on the 03 shock is what gets me, instead of messing with another kawi or suzuki shock with one, I will just ohlins the thing. Plus a bike that trick really deserves a proper shock to match the nice Showas on the front. My dad also setup the suspension and he likes it james stewart stiff. I have messed with the clickers, but I think the compression stacks are just too firm and rebound stacks too light. The bike simply does not settle into turns at all. It just jack hammers you to death. Dicks did the forks and shock originally, but as said, my dad had them setup, so they are a little shtiff.

As far as the offset goes, the 07KXF forks and OE trees have a 24.5mm offset, I would love to do some 22 or 20mm offsets to be able to slam the bike closer to the ground as well. I ran 22s on my 07KXF, should have taken them off when I sold that bike, I still regret that to this day. I think the KXF forks ruined the geoemetry as I would wager they are a good bit longer (we didnt measure head-tube to axle-center length and those OE forks have been gone for.. 14, almost 15 years now, so thats gone forever) If I had the bike in my possession I could dial the thing in a couple of months, but its not..

[SS109]

My buddy had an '03 and that chassis was a disaster from the factory. Once we became buddies, and he learned I was a bike mechanic, he enlisted me to figure that chassis out for him. It took me a good while of really digging in to that bike to figure out what the factory screwed up on the '03 when the '02 bikes were such awesome handling bikes. Triple clamp offset was the big one but also, as you mentioned, the lack of high speed compression was a factor as well. I would say that the offset was 90% of the problem.

I like fixing things on the cheap as I prefer riding over saving up for expensive parts. I would be looking for some OEM triples that will fit your forks but with the 22mm offset. It will really change how that bike handles. Literally, it's a night and day difference. Also of note, the '03 not having high speed compression, the '02 shock does have it and it bolts right in with zero mods. Just a quick cheap option available to you until you can snag an Ohlins. BTW, I'm an Ohlins fan boy, and truly love their shocks, so I understand lusting for one!

Of course, what you said about how your dad had the suspension done, that as well could be contributing a lot to the handling issues. Bikes need to sit down in the stroke (sag) the right amount along with the proper valving for the terrain ridden and the individual rider's style. Hope you get a chance to really get it setup correctly!

[smelonas]

I think in 2013 or 14 Kawasaki started fitting 22.5mm clamps, I will have to look into sourcing some of those. Some nice billet ones, like the ride engineering ones I had, would be sweet, but I can live with the factory cast ones if I cerakote them. haha I really wonder what a set of 20MMs would do. You could really get the bike short and tucked with those! I ride enduro stuff now, so the days of 6th gear pinned are all but gone, turning and good mobility are the name of the game now.

Good to hear from someone that actually dove into the 03 frame and has some experience with them. I will use that on mine for sure. For the longest time we looked for a shock with a high speed adjuster but we could never get an answer on length, fitment, etc. good to know that an 02 one will work. I will have to see if my local part-out'er guy has one lying about..

Ohlins and that beautiful gold anodizing is just too much for me to not have. Found a place a Europe that has a nice stock of them, so want to get one before they sell out and lead times become stupid.