Missing Quadrajet Vacuum Port: Plug or Replace?

[71GreenJunk]

I've got two quadrajets here I'm trying to build a nice one out of the two. I've got a '68 Chevy Quadrajet that's seized and I don't have any hope of saving it, so I bought a '73 Chevy Quadrajet off eBay that after my inspection looks pretty decent to me but the only issue I've found so far that im unsure of how to solve is that the vacuum port on the driver side just above the baseplate has been pulled out of the carb body. What is this port for? I'm really only needing ported vacuum for the distributor advance and to reuse the port for the choke pull off. Can I just plug it? The '68 carb still has the port in it and I'm thinking I could swap the port from the '68 to the '73 carb if the port is needed. The two carbs are essentially the same with the exception of the vent in the airhorn the '68 has and the '73 does not. Any advice on how to go about doing this? I'm afraid I'll get it out, put it in the other carb then it'll fall back out or not seal well. Maybe I'm over thinking it but I thought I'd try and get some advice from someone who has dealt with this before.
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[dmjlambert]

My truck had a carburetor that was in really rough shape. When I got into it, I started finding stripped threads, missing minor parts, and makeshift fixes done by the previous owner. I ended up ordering a carburetor from nationalcarburetors.com, and I sent the bad one back to them to get a core refund. It was surprisingly inexpensive, or at least I thought so. $289 and I got $60 back when I shipped the old carburetor to them. I was very pleased, and the new carburetor looks beautiful, almost like new, and runs great.

I don't know if that's the direction you want to go and I apologize if you find my post to be off topic because you really want to get your existing carburetor going. I thought you may want to know this is an option.

I've attached pictures to show difference in old and new for me, the new one looks a different because I asked them to send me one with an electric choke and they custom built it for me with the 1969-style throttle linkage. But I could have gotten a shiny new one in the same configuration as my old one. (EDIT: The one I got from National Carburetor is not new, it is remanufactured, but they make them look close to new because of the plating and re-finishing they do. I was surprised how good it looked when I took it out of the box)

[geezer#99]

Originally Posted by 71GreenJunk

I've got two quadrajets here I'm trying to build a nice one out of the two. I've got a '68 Chevy Quadrajet that's seized and I don't have any hope of saving it, so I bought a '73 Chevy Quadrajet off eBay that after my inspection looks pretty decent to me but the only issue I've found so far that im unsure of how to solve is that the vacuum port on the driver side just above the baseplate has been pulled out of the carb body. What is this port for? I'm really only needing ported vacuum for the distributor advance and to reuse the port for the choke pull off. Can I just plug it? The '68 carb still has the port in it and I'm thinking I could swap the port from the '68 to the '73 carb if the port is needed. The two carbs are essentially the same with the exception of the vent in the airhorn the '68 has and the '73 does not. Any advice on how to go about doing this? I'm afraid I'll get it out, put it in the other carb then it'll fall back out or not seal well. Maybe I'm over thinking it but I thought I'd try and get some advice from someone who has dealt with this before.
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You need it!
It's the ported vac port you think you need.
Swap the barb over.

[71GreenJunk]

Thanks. Tried to swap it over today. Used a pair of pliers to twist it out of the bad carb and just lightly tapped it into the decent carb. Seems to fit well, fairly tight in the "new" carb. Hopefully that will stay nice and tight and sealed. Think I'll use the ported vacuum to break-in the cam on my new engine and then I'll work on switching to manifold vacuum for the advance. I had got to reading about advance and remembered the '80s LM1s IIRC, that had a thermal switch that switched the advance to manifold vacuum when they started to get hot to cool the engine down and I do remember a big difference in how the old engine ran when I got it and when I pulled it, when I bought the truck the timing was retarded about 20 degrees and it didn't have a temp gauge then but I know it was running hotter and running much rougher than it did when I timed it to stock spec. I've had the same crate engine I'm buying and it ran 17" Hg vacuum at idle so I'm going to get an advance canister that is fully advanced at 15" or a bit less so the advance won't fluctuate. It'll be an interesting experiment if nothing else and if it doesn't work I can just switch it back. IIRC, the LM1 is pretty much the same build as the 350s that came in these trucks.

I'll have to look into national carburetor. This is about the 5th core I've bought to find a decent one. I'll have more in this than one would cost from them once I put new throttle shaft bushings in it and a good rebuild kit figuring in the cost of the parts carbs.
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[geezer#99]

Don't matter which port you use when you break in your cam.
With the rpm cranked up the ported port is exposed fully to manifold vacuum.

If you want a custom carb then look here.
https://www.smicarburetor.com/

[54blackhornet]

That is a very unusual looking Qjet they sent you ? Looks a lot different then the ones I've seen ? I like it though ! The one on my 71 is still not set up properly to run in cold weather, had the Carb Shop in Calf "Rebuild " it and quite experienced folks try to adjust it with little results....

[dmjlambert]

Originally Posted by 54blackhornet

That is a very unusual looking Qjet they sent you ? Looks a lot different then the ones I've seen ? I like it though ! The one on my 71 is still not set up properly to run in cold weather, had the Carb Shop in Calf "Rebuild " it and quite experienced folks try to adjust it with little results....

Yes, it is pretty interesting. Their part number is ND4478, so looking at their website it appears to be for 1981-86 Chevy trucks and the description is:

305"-350" Eng Non Computer
MOST COMMON

When I talked to the salesman who took my order, he was quite knowledgeable and helpful. He said they can't just add an electric choke to a carburetor that was designed with a divorced choke, and they had to build a different carburetor that was originally equipped with an electric choke, and they could build it with the linkages that would work for 1969. I have not wired the TH400 kick down and I don't have a switch and switch mount plate for it anyway, so I used the kick down power wire to power the choke. The electric connector for hooking it up to the carburetor came from O'Reilly's and it is BWD part number PT762. I plugged the brake booster threaded port with a threaded nylon plug from the hardware store, and plugged all the other unused ports using a variety pack of vacuum caps. I bought the lifetime warranty option on the carburetor, and they put a spot of tamper seal on one of the screws, so I think they expect me to never take it apart, and to send back to them for any repairs. I suppose I will talk to them when that time comes. All the settings were already made and it was engine tested at their factory, so all I did is set it on my engine, bolt it down, and connect it, and it ran great. I did need to adjust the choke because it was starting really rough in the mornings. The "upgrade" version with electric choke was $20 less than the original 1969 divorced choke Quadrajet when I ordered it. Since it was already unbelievably inexpensive, that was an unexpected bonus.