1 shock or 2? Performance differences?

[jgas]

I just bought a really nice, partially restored 79 KDX 250. It has dual rear shocks, with resevoirs built into the shocks, not what I expected, from what I remembered they were "remote" resevoirs with lines to the shocks. I have tried to look up pics of old DX's from this period and have found some pics with no reservoirs, some pics with remote, some like mine. I imagine some of the pictures I've found are of modded bikes with newer/MX/aftermarket shocks? I also have a beat up 81 KDX 250 with a single rear shock that needs to be rebuilt but is rebuildable. I am wondering if it would be worth the trouble to either swap the 79 motor into the 81 frame, or the 81 shock and swingarm onto the 79. From outward appearances the forks look identical, and the only frame differences I can see are minor. I could handle any welding needed for mounting brackets on the frame/swingarm. The 81 has the old school lever attached to the shock and swing arm.

The bigger question here is if there was a huge functional difference between the 79 and 81 DX with a single shock? I have ridden the 79 hard and found it to handle very well for an older bike, but it does bottom fairly easily in the rear. The bike feels well balanced and soaks up rocks and small chop a bit better than most modern bikes I've ridden, only seeming to give up suspension performance on big square edged hits and jumps. I considered changing the shock springs to stiffer progressive springs, but really just decided to either upgrade to the single shock or leave it alone since it works so well on the most common stuff that works the suspension. I won't be doing any big jumps, just trail riding, maybe an AHRMA endure, and AHRMA vintage MX.

For anyone like me that wanted to jump into the vintage bike racing, but was afraid that an older bike would beat up my already beat up old body, (having BAD memories of old bikes), it ain't so! Like I said, I wouldn't want to jump this old 79 bike over big jumps or flat land it, but it handles the usual trail riding, even 80% speed just fine. My 01 GasGas actually hurts my wrists, knees, and back a little more than the 79, and I'm almost as fast on the 79 in most terrain. Vintage is fun! And working on this old bike is easy too. Everything is so wide open and easy to get to! No radiators, no hydraulic stuff, simple and easy. Yes, as I expected the brakes ain't so great. Actually the drum rear is fine, the front has very little feel and takes a hard lever pull, but it actually works better than expected, just DO NOT FORGET THAT DRUM BRAKES SUCK WHEN WET! And this old 2 stroke actually has a little engine braking. No fear of stalling, revs slow, but you can use the engine braking a bit. I'd call it similar to an old XR 200 in engine braking.

[Julien D]

Not sure about the motor swap. Should swap right over without much trouble. I'm pretty sure the first KDX250 came out in 1980. The only 1970's model KDX I am aware of is the introductory 79 KDX400. The only difference I know of for sure between the 1980 KDX250 and the 81-84 is the rear suspension. The unitrak single shock should have a good bit more suspension travel than the dual shock setup on the 80.

[jgas]

My bike says 79 according to the vin, but others have told me they didn't think a twin shock KDX 250 was ever made in 79. It's possible someone put a 250 motor in an older mx frame. For now I'm going to try stiffer front and rear springs. My only complaint is bottoming the rear. Slightly stiffer front and back would be nice as long as I can keep the plushness on rocks and roots.

An old MXer I know said they made a really cool KX 250 in 76 or 77 that had an aluminum tank and near works suspension. He was semi-sponsored by a bike shop and they ordered it. He remembered someone saying only about 400 were made that year, but it was very fast for the times. Anyone know about this bike?