Vacuum Advance

[AustinDube]

So when I changed my distributor and carburetor I had no issues at all, I went with the $90 blueprinted distributors from summit racing and got a edelbrock 1405 carburetor. I was told to just put a screw in the vacuum advance hose, the hose plugged up on the side port of the old quadrajet but there is no port like that on the 1405. Im not sure if i keep it blocked or what! it runs mint right now anyways.

 

[vkh]

Well, I found a picture.

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I would suggest running it off the manifold vacuum, to my understanding the only reason oems started using the ported or "timed" vacuum was for emissions purposes. Here's a nice little article if our interested in alil more depth. http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm.

Oh and I would suggest running vacuum advance for a street car, gives you more advance at idle and cruise improving efficiency and dials it back under load.

 

[AustinDube]

Okay, but in a couple vids i heard that they had used the manifold vacuum for automatics, mine is a sm465. and it is a 76 k10 mostly offroading. will I have to retime it once i plug up the advance or?

 

[74 Shortbed]

Timing is always set with vacuum advance disconnected.

 

[SkinnyG]

You will have to adjust the carb slightly once you're running manifold vacuum - usually a tick leaner at idle. Idle speed will be higher too, so that will have to be adjusted down.

I've tried both manifold and ported on my engine, and don't notice a whole lot different in performance. I've stuck with manifold vacuum.

 

[Georgeb]

To sum this up:
1. Set your base timing at about 12 deg btdc with your engine RPM around 600.
2. Connect your vacuum advance to manifold vacuum.
3. Readjust your idle speed to the desired RPM.
4. Adjust idle mixture if needed. (I say it's needed but the procedure can vary
so I will leave that to another post.)

 

[rich weyand]

And here's all the whys and wherefores:
http://www.gmsquarebody.com/forum/showthread.php?t=14508