'71 Quadrajet vacuum port

[doublefive]

Hi Guys,
We recently build a '69 GTO 400. It came with RA headers and with a '71 RA Quadrajet. It runs perfectly but has a terrible noise under the hood. We found out that it's caused by the vacuum port you can see on the attached photo (circled in red). If we plug it, engine stalls and doesn't start again.
What's the function of that port? My buddy's '69 GP doesn't have that and there's no reference to that in '69 Service Manual. I think because it appeared later on Quadrajets (and this '69 GTO has a '71 model).
Could anyone help us, please?
Many thanks in advance!
Frank

 

[melsg5]

Best of my knowledge that is the port where the line ran to the charcoal vapor canister. How did you go about setting up this carburetor to run on this engine. With the port plugged, the engine off, did you gentle seat both mixture screws by turning them clockwise and then turn them both counterclockwise about 5 turns? You then start the engine, adjust the idle speed screw and then one screw at a time turn the mixture screws back in a 1/4 turn at a time, watch the idle speed on a tachometer, and continue turning in the one screw until you get a drop in idle and then back out the 1/4 turn. Then do the same procedure with the other mixture screw.

 

[avell007]

I am thinking more in line with a bad carb gasket between the top of the carb to the main body ... when you plug the port the vacuum sucks fuel from the bowl flooding it out..do you have to hold the gas pedal to the floor to get it to restart? After you unplug the port that is..
just a thought

 

[doublefive]

Thanks for tips Mel and Avell!
As I remember, after the complete rebuild (of course we built in new gaskets) we preset the carb according to the instruction of the '69 Service Manual (or Jim Hand maybe...). I think the engine starts (and runs) only incidentally with tihis setup.
We are going to solve the problem tomorrow... I'll inform you about the result and write some thought about the current setup.
Just one more question: In the case of a factory setup with charcoal canister, are there a continuous flow of air and gas vapour to the carb (with running engine of course) or not?

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[melsg5]

if you mean was there anything like modern vehicles, a solenoid etc. no, just the line running from the canister to the carb. It is possible that the port only has vacuum at idle. Can't see it in your picture but there should be a bowl vent on the top of the carburetor towards to front.

 

[doublefive]

Thanks, Mel!
In the end, the problem was very simple... At the first some starts after rebuild we have luck. We pre adjusted mixture screws but forgot the further adjustments. So engine started, has good idle (accidentally thanks to the extra air went through the unplugged charcoal canister port), revved up well - BUT had the horrible sucking noise. So we plugged the port. Engine was idling in this moment at the first time, so - of course - it stalled. We tried plugging the port again at higher revolution - of course engine didn't stall - gaskets are OK, bowl went is OK, etc. So we checked carb setup and noticed that the idle speed screw even didn't touch throttle lever - in that moment we noticed an other status: we are idiots
We plugged the port, reset mixture screws, started the engine, set idle screw and mixture screws... ta-da!!! Everythig is OK! Except me and my buddy
Thank for your help again!
Blaise and Frank

 

[melsg5]

I figured that it was mixture/idle speed screw related when you said it stalled when the port was blocked. Glad it was an easy fix. I just noticed you are in Hungary! Guess finding local experts on 60's American cars isn't too easy.

 

[doublefive]

In fact, the situation is not that bad in our country. Before 1990 it was really very difficult to find skilled professionals in this field. In those days to own an American car was the privilege of few chosen person (politicians, actors, etc.) and replacement parts or service manuals was virtually impossible to obtain. So just some old-school, war-hardened repairmen have the courage to service these cars... With more or less success. Most of these cars became junk but once you have seen one of them, you never forgot. So after the fall of the Iron Curtain when Hungarian people already have the possibility to get parts, literature, cars from the U.S., many "infected" guys seized the opportunity. Still in the absence of skilled mechanics (e.g. with proper English knowledge for understanding literature) almost every American car owner serviced their own machine, tried to help each other, and some of them became real experts (compared to the average). At that time I was a schoolboy and my buddy, Blaise owned his first U.S. car, a first gen Chrysler LeBaron. It worked nice so it didn't need much care. After than he bought a second gen Camaro. It was a real flat black rat garbage but with strong, reliable engine (and loud sidepipes, WOW ). So it didn't need much care, too. My pal's experience really started to grow in 2003, when he bought his first really impressive car, a '69 Grand Prix. As it needed to be an officially certified oldtimer car if Blaise wanted to use it in traffic, he had to restore it. In fact not so long after that did I get into the story, when he bought a '78 Corvette, too. I asked him to let me help with some repair in return I learned a few things about American irons. Shortly after I broke up with my girlfriend and bought a '68 Executive Sedan (why not ) from South California. Increase in the number of Pontiacs increased the courage to fully restore a '69 GTO. So in 2011 we bought one. By now we have learnt a lot but suffered a lot, too. It's a small country, so it's hard to find good bodyman who can do the body restoration properly (body spent a total of two years in three workshop (!)), paint shop, where mirror-like finishes are made, etc. The GTO is about 80% ready now and it's like a dream. A convertible matador red beauty with 400 and four on the floor. It's the one and only in Hungary and I think a car like this is also a big eye-catcher in its fatherland, too.
Returning to the difficulties, we were a bit frightened that something was wrong in the carburetor. We heard too much bad about Quadrajets so we asked first than started thinking Many thanks for help, again! And sorry for the long story (with not the best English)!

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[melsg5]

I appreciate the detailed history, it's always interesting learning about another automotive culture. Lots of luck with the car. if you can post some pictures that would be great.