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1968 DeVille Convertible (current project)
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Discussion Starter #1
Any tricks for a carburetor that won't seal to the manifold? I have tried 5 new gaskets, various spacers, etc. and I still have a leak around the base. It's driving me nuts because the engine won't idle properly.
Any ideas? Is there ever a time to not put the gaskets on dry (in other words, should I use a sealer?).
 

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1970 Sedan deVille hardtop
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595 Posts
The carb gasket should be put on dry.
Look at the gasket very closely. Place it against the carb base with the carb off the motor, and then against the manifold.
GM made dozens of different carb base gaskets over the years, and a number of various little channels in the carb base and the manifold togo with each one.
Lots of times, the generic replacements the parts store has aren't right. I had a real pain with a '70 Camaro I had with an exhaust heat channel right up at the carb mount. I kept getting gaskets that would either leave it unsealed and leaking exhaust under the hood, or open to the intake and choking the motor on exhaust fumes. Fortunately I still had the old gasket and could bring it in for them to match.

I am assuming this started when you tried to replace the old one? Do you still have it to compare? I'd suspect that the gaskets you're getting aren't covering a small passage in the carb base resulting in your leak.

You HAVE been careful tightening the carb down, right? It isn't all that hard to overtighten the front carb bolts and warp the whole carb. I've seen that done. Junked the carb - warped the air horn and main body to where nothing would seal.

As a last-ditch solution, some places sell gasket paper. It comes in sheets like notebook paper and of varying thicknesses and composition. Get some on the thicker side and trace the outline of the carb base onto it, then cut out four holes. That ought to cover everything that needs covering.
 

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94 Fleetwood Brougham
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7,534 Posts
Which carb do you have? AFB or Q-Jet? I think 67 was first year for Q-Jets. Pontiacs has some odd exhaust channel (like BlueEyes dealt with) that was up front just in front of the primaries. Possible Cad did too. I think they had a special gasket too. Take a look at a 1967 Pontiac 400 gasket. Get one from NAPA or a higher end parts store. Thicker gasket is needed.

Also, check that the intake isn't warped (chances are you could drop the Titantic on that intake and not warp it...) and that the carb base is too. A good straight edge and a feeler gauge is a good way to check. A thick gasket should handle around 1mm warpage easily.

Else like BluEyes said, make one, but be careful of that exhaust channel, it may burn up regular gasket material. I often reuse carb baseplate gaskets with 100% success (unless I tear it), and often double stack them when I get a new one to better isolate from heat.

Oh, I think 10 ft/lb is torque on a Q-Jet, not sure on AFB, but should be close.
 

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1968 DeVille Convertible (current project)
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Discussion Starter #4
It's a Quadrajet. The manual shows a thin metal shim that is supposed to go on between a new gasket and the carb. I don't have this and can't find it listed for sale, at least at the NAPA's Autozone, etc. The manual warns that the CAR WILL NOT IDLE WITHOUT THIS SHIM, just as I'm experiencing. Anyone know about this?
 

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1970 Sedan deVille hardtop
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Well, I know the manual (FSM I presume) is usually right :)

So, get some thin copper or aluminum and cut it into the right shape. Hopefully the manual shows what the gasket should generically look like? Otherwise just try to reason through what parts need to be covered, which don't.
If you have a problem sealing an exhaust crossover port, the "coppersafe" silicone RTV is able to take really high temps and might help if all else fails. Otherwise I wouldn't use any kind of sealant.

Ah, the joys of old cars and generic replacement parts! Just remember this in the future, and NEVER throw out the old parts untill the car is back running. Sometimes that old part is the only one you get...
 

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Isn't that year of Caddy supposed to get a Stainless steel shim? I know in my '70 manual it says explicitly not to use the stainless steel shim that was used in previous years.
 

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1970 Sedan deVille hardtop
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That's probably it then, finding it is going to be the trick.
I reccomended copper or aluminum because they are both readily available, and being on the softer side are easier to cut and potentially seal better. Heat shouldn't be a problem for either as some header gaskets are copper, and the carb baseplate is aluminum itself.
 

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1976 Eldorado project
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That's pretty weird...

However, I believe I have the shim it is talking about. It came still on top of the carb gasket on the '68 472 intake manifold I got. I can take some pictures if you like to make sure it's the right one. Then if you want it you can have it for free.
 

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1976 Eldorado project
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Alright, I took some pictures of it. It isn't the prettiest thing but I would say it will work...not completly flat but so thin that I think once you torqued it down it would be fine.





Theres pictures from directly above, at an angle, and then a shot of the other side.
 

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1968 DeVille Convertible (current project)
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Discussion Starter #10
That looks like what my manual shows! Do you have a PayPal account? Let me deposit some $ for shipping and your trouble!
John
 

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1968 deville
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can someone confirm the placement of the shim and the "paper" gasket.... i just bought a car (68 coupe) where someone figured these werent needed:bigroll:

ive located a shim and the base gasket, im just not sure which order they go on. to me the shim would go 1st then the paper (felpro) then the carb? can someone confirm any of this though

thanx!
 

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94 Fleetwood Brougham
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Sorry if I don't know Cads of these years, but Pontiacs had a exhaust gas passage under the carb. So it took a special gasket that could handle it, probably the shim. That passage was discontined for Pontiac in 1968, it was a one year only deal

So you need a gasket and then the shim and another gasket min. But it needs to be a 1967 gasket. Look at what Pontiac has for 67, might help.


can someone confirm the placement of the shim and the "paper" gasket.... i just bought a car (68 coupe) where someone figured these werent needed:bigroll:

ive located a shim and the base gasket, im just not sure which order they go on. to me the shim would go 1st then the paper (felpro) then the carb? can someone confirm any of this though

thanx!
 

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1968 deville
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from what ive found they only call for one of each, so i dont understand how i would have 2 normal gaskets and a metal shim?

and albymangled what you have in those links is exactly what i have for my car g796 looks exactly like my metal shim and g596 is the "normal" gasket my car calls for.

i just need to get a final answer on the location of each:banghead:
 

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1970 calais coupe
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346 Posts
Ok, this is my opinion only but here goes...

manifold. metal shim. gasket. carb.

but....if anyone has a factory manual showing different I'm happy to be proven wrong...

mebbe call?

Questions and Information (253)833-4105
Order Line 1-800-994-CARB (2272)

CARBS UNLIMITED INC.
727 22nd st NE
Auburn Wa 98002

come on guys....who's got a factory manual for the 1968 Deville?
 

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1968 deville
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5 Posts
thats my thinkin..... hopefully someone will know for sure soon, my new carb (rebuilt from holley) will be here in a couple weeks.
i just changed the timing chain, water pump, and such this week. car runs pretty good, but you can literally hear the exhaust exiting at the carb base and blows out what appears to be exhaust from it. the car has 35k miles but someone had messed with just before i got it, i believe they removed the gaskets while cleaning the carb
 

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1968 deville
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fyi....holley doesnt build these carbs anymore:bigroll:
after a month of waiting i was called and told they werent gunna do these anymore and that my order was being canceled and have a nice day...gee thanx

im still wondering if anyone can tell me for sure bou tthese gaskets... surely someone has a manual or has done this before....lil help please
 

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'85 Fleetwood FWD
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728 Posts
Which model Holley did you try to get?? I see that Summit has two spread-bore Holleys to replace the Q-jet.

They may even know about the shim for the base. You could call them and ask.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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I would buy a used carb or two on Ebay and have the best one rebuilt by an old timer and it should work as good as any new one.

I was under the impression that the metal shim/gasket was actually a heat shield and I pictured it in my mind to be larger than the carb.

I just looked in my oldest motors manual and there is an actual blowup of the 67-68 carb and I don't see anything different than any other Quadrajet. This Motors was dealing with individual components, ie carbs, and didn't show the metal shim/heat shield. I don't understand why that metal shim is so important but it has been verified in other posts here before. Anyway there shouldn't be any problem for an old time mechanic to rebuild one.
 
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