Vacuum Advance plumbing
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Elder User
Joined: Sep 2006
Posts: 519
Likes: 1
From: Bountiful UT
Vacuum Advance plumbing
Hey all I am stumped. My buddy at work has a 77 4x2 with a 302, His vacuum advance is hooked straight to manifold vacuum. I went out today to try and help him plumb it correctly and there are NO vacuum ports on his carb?? it is a stock Motorcraft 2 barrel. Any ideas as to why there are no ports? and how do you hook up the advance without them?
I am wondering if they got broke off or something? I have never seen a carb without ports. BTW he is the second owner, (his dad bought it new)
I am wondering if they got broke off or something? I have never seen a carb without ports. BTW he is the second owner, (his dad bought it new)
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Elder User
Joined: Sep 2006
Posts: 519
Likes: 1
From: Bountiful UT
Thanks, I don't feel so stupid now, I went out to show him the ported connection and nothing there, I am going to have to look closer monday, I am betting they got broke off at one time or another and that is why he can never get it to run right.
Elder User
Joined: May 2002
Posts: 927
Likes: 3
From: Lake Point, Utah
Should have one back behind choke area or down on the base plate in front (I'd have to go out and look at one to be 100% sure..but let me know if you need me to)...If nothing else...pull the carb off...generally you can reuse the base gasket unless the thing is 100 years old and breaks.
Junior User
Joined: Jun 2010
Posts: 86
Likes: 0
From: Sulphur LA
My vacuum advance is hooked up to manifold vacuum and the truck runs good. Am I missing any performance or power with it hooked up to manifold vacuum? What are the pros and cons? The truck has a 460 with edelbrock 750, rv cam and msd ignition.
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Elder User
Joined: Sep 2006
Posts: 519
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From: Bountiful UT
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Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
You should be pulling ported (timed) vacuum for all over best performance, the only need to pull manifold vacuum is if you have a radical cam you need to tame to achieve a decent idle, ported is the way to do go on a stock and/or mildly built motor.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
What is your initial timing set to currently? Since connecting the vacuum advance to manifold vacuum instead of ported vacuum increases the timing at idle, your timing at idle will change when you change the vacuum advance source. You will probably need to adjust it for the difference.
Junior User
Joined: Jun 2010
Posts: 86
Likes: 0
From: Sulphur LA
The truck was set up like that when I bought it so I don't know what it is. I will admit that I don't know much about timing an engine. I noticed that my advance was hooked up to the manifold just the other day and reading this thread got me interested in it. I already have a 460 so gas mileage is not great as is but I don't want this to affect it negatively. Does it affect mileage and power? Mainly, I just want it done right. I love this truck, it never lets me get bored!
Elder User
Joined: Nov 2003
Posts: 778
Likes: 2
From: southeast Idaho
I run mine from the manifold on my 460 as it idles better and a little cooler and helps keep it from predetonation as the timing backs up a little when accelerating. I like it that way and one article around here somewhere says it should be run that way.. Its whatever you think works best for you really
