Originally posted by Henry Rifle
Brian,

Most HEI distributors require ported vacuum - that is, a port above the throttle blades. With the engine at idle, find a port that has zero (or practically zero) and hook your vacuum advance line to that one.

Find another port that will suck the chrome off of a trailer hitch and attach your modulator line to that one.
henry, I'm not sure you're right when you say most hei dist. run ported vac. i haven't read anything on this in about 25 yrs, but I've set the timing on a lot of cars in that time. you have to pull the vac. hose off of the vac. adv. before you set the timing, so the timing can retard back to base timing. if it was ported vac. it wouldn't make any dif. when you pulled the hose off. 9 out of 10 gm cars idle down when you pull the hose off of the vac. adv. and all you are doing is changing the timing im talking stock setting. that my story and im sticking to it. help denny where are you at?