Air pump vac line

[James B.]

I just put a smog system back on my 69 400 hp. With air.
i was wondering were the correct place to hook up the vacuum line.
i am running full vacuum not ported. Could I use the plugged off
ported vacuum port? Or should I put another tee in the choke pull off line.
thanks for your help. Not a big deal just wondering.

[Robert S.]

Re: Air pump vac line

The diverter valve requires full time vacuum to function properly. There should be a T-connection on the line from the center carb to the choke pull-off.

[Duke W.]

Re: Air pump vac line

Both the AIR diverter valve and choke vacuum break signal lines should be connected to a full time manifold vacuum source, so teeing into either will provide full time vacuum to the VAC.

You should also check the specs of the OE VAC (and determine if the installed VAC is OE equivalent or something else) to ensure that it passes the Two-Inch Rule.

Typical L-36/68 idle behavior with an OE equivalent cam is 15" @ 600 with a manual trans, and a bit less with an automatic, so in most cases, the 12" B26 is the best functional replacement.

The other method is to modify the center carb base plate by lowering the port to below the throttle plate, which usually involves plugging the existing port with a piece of lead shot or epoxy and then drilling another hole below the throttle plate. I'd have to inspect the carb myself to be sure how to do it, but I recall that others have explained how to do this on a Holley four barrel, and the two barrel is probably similar

This makes the conversion to full time vacuum advance invisible.

Duke

[James B.]

[James B.]

[Chris H.]

Re: Air pump vac line

James, here's how the factory did it. You can see the "T" in the choke unloader. That line goes to the AIR pump diverter valve. I notice that your carb base ported vacuum tap for the VAC is plugged. That is why you currently have 2 "T"s in the choke unloader line. What I did is drill a new hole in the base plate to allow true manifold vacuum to the VAC. This mod uses the old ported manifold tap so it looks factory.

[Chris H.]

Re: Air pump vac line

James, rereading your post, if you're referring to the white "T" in the middle of your photo, that's the carb throat vacuum line from the primary that actuates the vacuum diaphrams for the secondaries.

[Duke W.]

Re: Air pump vac line

Thank you for looking at this Duke,the number on the can I am using is 360.
i moved the vac line from ported to the choke unloaded a few years ago. So I already have a
tee in the line. I was trying to avoid using another tee in this location. Before the car wouldn’t even idle
with the air cleaner off. No it starts right up and idles anywhere from about 600 on up. Seems to work fine.
just not sure about this 2nd tee. Thanks again.

It should fully read MS 360 12, so it's probably original. Specs are start @ 6", 12 @ 12". The B26 has the same start point, but max is 16 @ 12". The additional 4 degrees should not cause a problem if it ever needs replacement, and both should pass the Two-Inch Rule if the camshaft is OE equivalent.

Duke