Technical from ported to manifold

Hey all,
After reading all of the excellant advice here, I've decided to go from ported vacuum to manifold vacuum on my motor. (SBC)
So I can swap the hose over no problom, right? But that's gonna add alot of advance @ idle, So what's the proper method to get it all dialed in again?

 

Idle speed will shoot up, and you will have to dial it back and confirm mixture screw adjustment

 

Time it and forget it, if you are coming in too fast adjust your vac can. If you don't have an adjustable vac can get one they are cheap.

 

Based on my own experience, you will probably want to keep the static timing at Idol with vacuum disconnected the same. Otherwise it will bog terribly off the line.
I set mine at 8 or 10 degrees (vacuum disconnected) and then adjusted the vacuum advance down a degree at a time every time I drove it until all part-throttle ping went away.

 

Forgive me but, I wanted to do this too but I am not understanding.
If you go to full manifold vacuum, you are using all the vacuum advance available until centrifugal advance kicks in, so what exactly are you adjusting with an adjustable vacuum unit?

 

I've read a ton on here and other places about this. I know GM had used manifold vacuum and why, what I wonder is , could it have been used because they had only 4 BTDC( initial) some of those motors, and they needed he extra timing to keep it cooler? Most performance sbc's use 8-10-12-14-16 initial .No dog in this fight I'm not using vacuum at all...

 

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

 

Thanks all for the tips and info.
I had just read through that today. (bout three times to make it all sink into my thick head.)
Funny thing struck me,when you set your timing the rule is to disconnect your vacuum advance and plug the line right? But if you're using ported vacuum, at idle there is no vacuum in the hose so no need to plug it. Rule is meant for manifold vacuum where there is plenty of vacuum at idle.
I'm gonna change my vacuum canister this week and crank the idle way down and see how it goes. My motors been running hot and I'm hoping this helps lower the temps. They say it will.

 

To add, my carb and distributor guru says to always run manifold vacuum. He says you are leaving some fuel economy and power off the line on the table if you don't.

To paraphrase:
That little bit of time between when ported vacuum drops before the centrifugal advanced kicks in is where some performance is lost.

Take it for what it is but I've had excellent results with everything he's ever done for me.