Help, Having trouble setting the timing..

I have a '74 Gold Duster with a 318. I have changed the air intake manifold and carb to an edelbrock 4-barrel 1406.
I am trying to set the timing because I know it is off. My idle is set at about 750-800 rpm when at temp. my problem is that when I set my timing light up and then pull my vacuum hose to my distributor it dies. How can I properely set my timing if this continues to happen?
Any suggestions?
Author: 74GoldDuster