235 - 216 Distributor vacuum advance

[Fred n' Ethel]

I have a 39' 216 and a 54' 235.
Both are ported vacuum to the distributor. Stock.
Both work .... but a bit differently.
The 216 responds immediately and smoothly to an abrupt acceleration. No popping, hesitation just perfect.
The 235 however does not advance the dist. immediately or to its full extent so therefore there is a slight hiccup, hesitation or pop when abruptly accelerating.

The timing is set by the book for both and run excellent in all other regards.

The only thing that is definitely different is the return springs in the dist vac pots.
When squeezed together by hand, the 216 is much lighter than the 235.
I put a little "helper" spring (rubber band) on the 235 dist to assist the pot and it performed better, much like the 216, more immediate and responsive.

Everything is lubed well with complete freedom of movement and all vacuum tests look good.

Questions:
Were there different springs used in the dist. pots ?
If so, is there a procedure to select the proper one ? ie. should the pot pull at a certain vac. ?

Or, any other suggestions welcomed.
Thanks for looking.