Everyone has their own preference depending on engine. Just for comparison, here's mine if you are "trying different methods". I'm more of a Big Block person but here's what we used to do at our shop on our track and high perf street cars.
Always verify the initial throttle plate adjustment on your carb. I can't tell you how many I see where the throttle plates are open past the Ported Vacuum port (to increase idle - incorrectly). The owner now re-assures himself that "Ported Sucks" because of this and they have no idea that the throttle plates are open past the ported vac port and the carb is now our of the idle circuit. Incorrect main jetting with this scenario is common as well. There I see lots of Holleys with a bypassed idle circuit, lower vacuum and bigger jets to keep it idling (roughly I'll admit). Once your carb's throttle plates and base jetting is set, you can begin.
Quite a few older SBC engines can and do run quite well with Manifold vacuum source. I prefer ported but a few friends do not. I think many people like to "over do it on initial timing" and then use manifold vacuum. They then see that it's not correct., scrap the whole idea, use ported and then do the "Time it by ear method". - Never really understood that one....
Keep in mind that depending on application, Advance curve etc, that ported vacuum may cause pinging and higer running temps when you are doing the initial setup on the engine / carb.
Ported vacuum sometimes may be (and often is) needed for many EGR equipped engines, to increase combustion chamber temps to burn off more unburned hydrocarbons. This differs slightly in Non-EGR applications.,
A good tip that I've found find to be very helpful (SBC and BBC's at least) is: Initially, Any engine that has its vacuum advance sourced from ported when it calls for Manifold Vacuum, and runs better with it, may/ usually does have a timing problem ( THE MECHANICAL ADVANCE CURVE MAY NOT BE CORRECT).
On a SBC, you could try setting and baseline at between 8 to 10 initial, then set an adjustable Vac Advance for an additional 8 to 10 degrees @ manifold vacuum. Depending on Engne, this will usually result in a "runable" baseline to begin. (and many times can stay this way (for the street).
Mechanical curve would be appx 22 degrees, starting 100 - 200 rpm over your "out of
gear" or in Park idle speed",
Depending on compression ratio, cam, stall speed, etc. This would give 30/32 total
timing which should be more than enough for a SBC. You can then fine tune if needed (if you get Ping etc).
I find very, very few engines, street to mild strip, that don't like
properly applied ported vacuum advance. I see quite a few engines with the vac advance simply "torn out" and the owner is convinced that it's not needed on a street driven car. (Never really got the idea of this either.)
[This message has been edited by 3084me (edited 04-25-2005).]
