TOPIC:

Is this the advance curve you are talking about?

No, the advance curve is a graph that shows ignition advance in relation to engine speed - the faster the motor spins the more the ignition is advanced until the wheights hit their stop

 

Maybe you could take various measurements of the spring, then try to find a close match. Length. diameter. wire diameter. number of coils. that sort of thing. Do a search for how to measure a tension spring.   There was a KZ650 on EB a couple of weeks ago that appeared to have non-stock springs: silver in color & the ends didn't look stock. The springs looked like off-the-shelf from a hardware store or something; the springs are normally black, probably an alloy that resists rusting.  or keep it simple and get the parts from Z-Power UK. hee.

ps:  there's a KZ400 advancer on EB for $35T. It's kind of rusty but the springs look good & it'll probably clean up just fine.  there's another one from the UK for a bit more but it's in good condition.

I made this one out of parts from cheap ones I found on eBay. Can only use the springs and arms that came with them The backing plate pins are in different places so they aren't interchangeable. I tried the heavier ones then the smaller ones and came up with an advance that acted like it should with a timing light. The larger ones advanced too fast so I used the smaller ones. I bought a new one from Z1E for $150+ and its the same as the one I came up with only it's new. With both the idle is steadier and the bike pulls clean all the way to redline. 
Steve
 

I bought the advancer from the KZ650, the curve looked similar to the one from the 440.  The curve for the newer bike (82 kz440) has a range for the timing, (as seen above in the post by wookie58).  The notations on the curve for the 650 are the middle values of the range for the 440.  I am planning to use just the springs from the 650 advancer.  Does that sound reasonable?

Are the weights the same size (transferable) as they also work together in unison with the spring rates to give the desired curve (you could always check the weights when your good lady is out on her kitchen scales to compare the originals with the 650 items) 

I should check in more often.
1) SWest your work bench is cleaner than mine.
2) The KZ 650, 550, 750/4, 900, 1000 will not work on the KZ400/440 because they turn in the opposite direction.
3) I wouldn't get to hung up on the factory advance curve. Gasoline is not what it was 15 years ago let alone 40 years when these bikes were new.