buick 455 running on after shut off????

I installed another type of TVS switch that when engine is cold will open ported vacuum to the vacuum advanced but when engine reaches the normal temperature it will switch the advanced vacuum to manifold vacuum, with this setup I can close the throttle plates on idle when engine temperature is normal and prevent non necessary advanced when engine is cold. when engine is cold idle controls by choke and fast idle cam but when engine is warm idle controls by idle solenoid so when I shut the engine off solenoid will be off too and throttle will close completely and prevent dieseling.

 

I used it only because of preventing 30 degrees advance on cold engine on low RPM and choke in position (10 degrees initial + 20 degrees vacuum). If such advance not cause a problem I can delete the TVS and send direct manifold vacuum to the vacuum advance.

 

I tested the engine yesterday with vacuum advanced connected to the manifold and low range RPM power gets better and engine seems more calm in hot degrees but mid range RPM power goes down because of lack of vacuum in manifold in mid RPM also the fuel consumption around 50% or even more higher I guess because of timing. So what is your opinion to give it more initial and connect the vacuum advance back to the ported? how much higher than 10 degrees factory initial is safe and how much total is safe for 455 stage 1? or maybe should I use lighter springs but I guess I should go for way lighter to activate them on mid RPM.