Timing and Vacuum Advance 101

[cncsparky]

Written by a retired GM engineer 

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

[circleD]

 

[legomybago]

Thats good write up, leans more towards direct manifold vacuum vs. ported. i've always used ported, it's what I know. My first FMC I purchased a couple years ago ran goofy...they had it all out of whack, the carb was toast to start with, the distributor was in 180* off, they had the dist. advance plugged into full manifold vacuum. Well, when you press down on the (dual hydravac) brake system, it takes a fair amount of vacuum out of that motor, and thus changes your idle condition. The engine timing retards so far it barely would run, so I changed it to what I've always known...ported vacuum, and it ran great. I believe there is a rhyme and a reason to both set ups though..