What cam is in this motorÉ Big duration need much more base timing at idle.
get this by shortning-limiting the mechanical advance curve limit stop.
Stock distributor is about 20deg,, you want around 10-12deg limited mech advance.
This will allow you 22 to 26deg inital base timing at idle. while avoiding excessive WOT advance.
Just about right for most street cams with 224 to 240".050.
if the cam is really racy (240+) you will need even more base timing at idle.
lock out the distributor mechanical advance.
Check the timing tab for correct true TDC location using a piston stop.
There are three different timing tab --balancer combos.
This will allow you to get the throttles closed down more at idle and active idle mix screws.
You cannot achieve the correct timing curve for a stable clean idle by advance spring swap and vacuum advance alone.
Give it the base timing required by shortening the mechanical advance curve limit.