Pity there's no original info around. If it does go there as a top out spring it might be to slow down the return rather than bang into a very short few turns of top out spring. & maybe the damping design of the new damper rod matches all that somehow. I you could compress it fully without getting hit in the head by it escaping the bench vice it'd be good to see the compressed length compared to original--still going to be quite a difference though. How does the damper rod length compare to original. Other thing too is the forks will have heaps more preload from being held about a third or more further down when topped out with top out spring compressed. Might be for road riding or roadracing, shorten up the front end trick.

Ah … ok …. 
So use the original damper lower spring with the new cylinder comp and replace the top metal spacer with the spring ….
Cheers
T1 

Stacking springs will always give you a lower spring rate.  In other words, it will take less force to compress fork every additional inch. 

Could increase "preload"...  but excessive preload is not a good thing in my experience.

I bought one of these kits many years ago.  I could never make it work.  I put it back in the box and it is neatly stored on a shelf in my shop.  
 

Yes as MarkT says. I was just dreaming up ideas & for a start would depend how much longer than the spacer the spring 'is'. Tried all sorts of silly tricks over the years compressing from a great height then having topping out with a clang & probably coil binding on compression. One of our competitors on a TM250 preloaded his by so much it broke the top off the damper or something like that so it sunk to the bottom, topping & bottoming unsprung for a lap & still went faster than us. Think we were afraid to try & pass haha as all over the track.

Reminds me of the 'helper' springs I found inside the top of the forks on my DT400. Don't know if they helped or not.  

I remember a magazine article on this kit...  not sure if it gave details or if I still have the old magazine. 

If I come across it I will post it here. 

Please do Mark, I have about four sets of forks I could put them in to see if they work.  I will do some digging too, I have lots of old magazines catalogued. 
 

I found the article in the December 1970 issue of Modern Cycle.  Unfortunately, it's mostly about the company and how their kit gives you more fork travel and stiffer forks and not instructions.  Sounds like you just replace stock parts with kit parts.

The kit has modified metering rods that increase fork travel.  As far as I can tell, the longer springs replace the original long springs. 

Here is the photo and caption that shows the most. 

 


.

 

Thanks Mark, I will pull my kit out again and look at it, but I recall that there was nothing logical.  I probably have 2 forks that are not on bikes that I can try it out on.  IF I have any success I will post what I end up with.  I am not a good mechanic, but I can rebuild forks (and carbs) in my sleep but I could not figure this one out the first time.

Mike