# Vac advance port



## rheckman (Aug 28, 2018)

Ok,
I'm sure this has come up multiple times but here goes.
Because the PO left vac advance hanging off dizzy advance canister,I don't know where it should go.
There is a t off the rear base of quadrajet,with a capped nipple,can it go here or is there a specific spot.
Lots of different takes on this...
It's a 1970 ram air stock quadrajet.
Thanks,Bob H


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## BearGFR (Aug 25, 2008)

Hey Bob..

'The factory' configuration used a ported vacuum source. This is a source that comes from above the throttle plates and won't "see" manifold vacuum until the throttle is opened some. In the real world, use which ever source (ported or unported) that your engine seems to "like" the best. Remember that the correct way to set ignition timing, regardless of which source you use, is to disconnect the vacuum connection from the distributor and plug the hose so that it doesn't create a leak into the intake/carb.

How to identify which is which? QJets were made for a long time and there were a lot of different versions. The easiest way is to get yourself a vacuum gauge and connect it to each different vacuum connection on the carb with the engine running at idle. If the vacuum reading is very low or zero, you know that particular connection is for ported vacuum (sometimes called "timed" vacuum). If you get a significant reading (usually well above 15" for a stock or nearly stock engine) then you know that's an unported manifold vacuum source. Those are the only two "kinds" that there are, regardless of where they're physically located on the carburetor.

The big one on the back that's T'ed usually has the larger of the two going to either the power brake booster or sometimes the PCV valve (depending on year), and the smaller one going to the automatic transmission vacuum modulator. That one is going to be an unported manifold vacuum source.

Bear


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## geeteeohguy (Feb 2, 2008)

A lot of the earlier cars also used a hollow carburetor hold-down stud as a manifold vacuum source for the advance can. Easily installed if your carb lacks the fitting. My '67 with Quadrajet has one that runs the idle dashpot.


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## rheckman (Aug 28, 2018)

Thanks Bear,

There seems to only be 1 port on the front of this qjet,for secondary I think.
And the t off the back,3 port tee,only one plugged with what looks like the other end of vac advance line with a screw in the hose.
Nothing on front or sides,
I will see when I put dizzy back in.I pulled dizzy to put in pertronix,found some play in metal platform where points bolt on,
But I think it should be ok.
I'm trying to get to heart of problem with hard starts,idle issues,and shutting down when throttled.
Didn't start off that way when I got. It but is now.
I want to rule out points,then look at carb,maybe fuel pump after that.
I also found a crack in flange in dizzy base where clamp goes,I may weld it just to be safe.

Thanks,

Reg's,
BobH


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## rheckman (Aug 28, 2018)

Interesting,this is a 70 where would this tube be if there were one?


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## rheckman (Aug 28, 2018)

Interesting,this is a 70 where would this be located on carb if there were one?


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