Lets talk about Vacuum Advance.

[jorgensensc]

When you hook the Vacuum advance up to the carb, and vacuum is created, does that advance the timing and if so help me understand the concept. Full vacuum is at idle right? So at idle does it advance the timing, then reduce timing as you drive/ accelerate? This doesn't make sense to me (not much does I think). If you over advance your dizzy when you are setting timing, It will have a hard time cranking, but it tends to run better at speed and has quicker response (Unless you way over advance it and then you get the popping in the carb, etc). So why would you want the timing advanced at idle and reduced at speed? Or am I completely Backward in my thinking. Also on the carb I have always been told that the dizzy advance is supposed to be plugged in to the carb port that is NOT Manifold vacuum (usually on Edelbrocks the drivers-side), however I have always been told to use the opposite port (Passenger-side), the constant manifold port for better performance. Can someone please shed some light on this?
Shawn

[Cyclone]

Should be no vac at idle, then vac as you increase throttle, its called ported vacuum. should not be connected to manifold (constant) vacuum.
Get a cheapy vac guage and read all your ports at idle and full and partial throttle, you'll find the ported one.

[jorgensensc]

Okay, here is where I am lost. Does the ported vacuum work opposite of the other ports? I always thought there was vacuum at idle and as the throttle went up the vacuum went down. Am I wrong?

[Cyclone]

There is ported vacuum only when throttle is opened. Manifold vacuum will be there at idle/cruise and if you
crack the throttle quickly you will see the vacuum drop alot then retur to whatever your idle vacuum was. Clear as mud huh?

[68gmsee]

I read about vacuum advance sometime back. Here's a couple of sites to explain it.

http://www.2quicknovas.com/happytiming.html

http://www.highperformancepontiac.co...ech/index.html

Here's a short piece...

The carburetor is designed to provide minimal amounts of fuel and air in light-load conditions such as part-throttle cruise. But because cylinder volume doesn't change, the molecules within the chamber are not as tightly compacted, resulting in a less combustible mixture. Not only is such a mixture more difficult to ignite, the flame spreads slower, delaying peak pressure. For maximum performance in these conditions, spark must occur even earlier, sometimes in excess of 50 degrees BTDC.