[zeke67]

I agree with the above comments. Springs adjust the rate, the bushings limit how far the weights can move. (Note: if centrifugal force can't overcome a strong spring on a light weight, then that will be a de facto limit).

Get your total (vac advance unhooked) adjusted first to 36*. Adjust the springs to get all timing in by 3000 RPM. See where your initial falls. If initial is too low and you need more initial advance for good idle quality (as much as 16-18* with a performance cam) then you need to crank up the initial and use bushings to limit the total. The sum of initial advance setting plus mechanical should sum to 36*.

 

[zeke67]

I think one heavy and one light spring adds a "knee" or "break" in your timing curve where you have one rate for part of the RPM range and then you have another come in at a higher range. This isn't a bad thing for a street V-8.