Is this where I hook up Vacuum Advance on a Holley 4160?
 

Holley 4160 Carb (Vacuum Secondaries/Electric Choke/600cfm/"Smog Carb")
Note: Although this is a smog carb, there's nothing smog on my truck...
I've had my vacuum advance hooked up in the pictured spot for a while now, and my truck has always had an idle problem. I was at the drag strip yesterday, and a few people had their vacuum advance hooked up in the spot I have an arrow pointed at.
So which port should I have my vacuum advance hooked up to? The white circle/blue arrow one, or the red circle/white arrow one?
:confused:

For a vaccum advance there are 2 ways you can hook it up.

1. With vaccum going to the vaccum advance at idle (manifold vaccum)
2. Without vaccum advance going to the vaccum advance at idle (ported vaccum).

Pull off the vaccum hose when your truck is idling and stick your finger over the hole...if it tries to suck your finger in, you are running it off of manifold vaccum. If there is no vaccum at the port, it is on ported vaccum.

If your truck has a rough idle and the advance cannister is hooked up to the ported vaccum, hooking it up to manifold vaccum will significanlty improve the idle quality. From what i understand, there is no difference in fuel economy or power either way.

Try hooking it up to the manifold vaccum port and i bet it will idle much smoother. I'm guessing you have it hooked up to ported vaccum right now (i'm not familliar with Holley carbs).

I asked this question a while back tim. The only thing that full-time vaccum does is help with the idle. I run mine off full time, especially in the winter when its cold. But theres no MPG differences or anything.

Hmm..ok, Cuz it never idles the same. It's always idling all over the place. Like, sometimes it'll be smooth at 700, but then sometimes it's at 850..600..it's always changing. I'm gonna swap the source in a few minutes and see what happens...

Its definitely more lopey with ported, but in the winter its really not better.

My friends say that my truck idles really high in park and I just tell em its my choke and vaccum. Damned newschool kids and their fuel injection :D

Im just too cool for school I guess.

How high? 1000? What's it idle at in drive with your foot on the brake? (But of course, I don't have power brakes, so mine might be able to idle a little lower)

Try adjusting your idle with the vaccum guage....i found this is the best way to get a glass-smooth idle. If it is mis-adjusted it will surge alot like you have described.

The only time to use the ported vacuum feature on the carb, would be if you had a functional EGR. (That would be the white circle/blue arrow in your picture).

It's best to run full manifold vacuum to the vacuum advance. The KEY is - you have to either run an adjustable vacuum advance (such as the Crane unit), or limit the travel of a stocker. Obviously, the adj. unit gives you more flexability!!

With the vacuum adv. off and plugged - set your initial timing to 10*-12*. Hook up the vac. advance and dial in the advance cannister to give you about 8*-10* more adv. See how that works for you....pay attention to pinging.

Next thing to work on is your total timing. You need to see how much mechanical advance you have and how soon it's coming in.

I'm more familiar with timing for Buicks - we shoot for a total of 32* or so, and have it all in by 2500rpm. Pretty sure Chevy engines like a little more total timing.

OK, well, I DO have the Crane Unit. I have 36º by 3000. I plugged the ports on the carb and stuff, and set my inital timing to 8º. (Per Crane's instructions), then hooked everything up, and voila. But all this time I've been running off ported vacuum. I'm running full now. I will adjust if I hear pinging.
I think my idle problem is just my stupid carb (being a smog carb and all). I'm gonna put it on a shelf, and swap in a NORMAL Holley 650cfm 4160.

the top port is ported vacuum and the bottom one is full manifold vacuum