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Thread: Carb gasket differences

  1. #1
    Deeznuts08 is offline Cadillac Owners Member
    Automobile(s): 1968 Coupe DeVille
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    Carb gasket differences

    My car is a 68 coupe deville but I recently researched and determined the engine block is a 71. I need to know which carb mounting gasket is needed for my setup. At napa they have a gasket for a 71, which is different from the one they have for a 68. My intake manifold has the u shaped port for the exhaust to warm up the bottom of the carb also, I could not get that pic to upload though. Could having the wrong gasket cause the carb to not work properly? Could it cause the idle mixture screws to be ineffective? Could it cause it to bog at WOT? Thanks for the help?

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  3. #2
    Deeznuts08 is offline Cadillac Owners Member
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    The picture on the left is the gasket that napa auto parts says is for a 71.

  4. #3
    CADforce69 is offline Cadillac Owners Connoisseur
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    Re: Carb gasket differences

    According to Rockauto, the left gasket is for a '71 and the right is for a '68... The question is Which carb have you on your engine: 68, 71...? Serial number could give us a clue.

  5. #4
    Deeznuts08 is offline Cadillac Owners Member
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    Not sure which number is the serial number. Oreilleys, autozone and car quest all said the same as napa. I'm gonna try it and see the difference cause right now I can't figure this out and it's frustrating.

  6. #5
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    Re: Carb gasket differences

    The serial should be behind the main housing, behind the secondary throttle plate linkage. If it's a q jet. Depending on the carb to it won't run right with the wrong base gasket.

  7. #6
    Deeznuts08 is offline Cadillac Owners Member
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    So, I've tried both gaskets and neither one has changed how the carb performs. Screwing the mixture screws all the way in or out changes nothing. This is really stumping me. The timing is set right, the plugs and wires are good, the points,cap and rotor are good. The car will idle fine and rev up ok until the secondaries start to open, then it bogs and sprays fuel up out of the carb toward where the air cleaner would be. When driving the car, it feels very underpowered. I have changed a bunch of vacuum lines and don't know where to go from here. Two carburetors from the same place and the same problems on both which leads me to believe that it is not a carb problem. Both rebuilt carbs from a place called carb exchange. Any help please.

  8. #7
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    Re: Carb gasket differences

    One of those gaskets should be right. Is the butterflies opening on the secondary? Make sure the rod is connected that open them on top of the carb, this is how the secondaries are metered. Is the float set right? Does the secondary butterflies have tension?

  9. #8
    Deeznuts08 is offline Cadillac Owners Member
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    All of those things are ok. Thanks for your help caddygas. I am going to do some more wrenching on it next weekend. Hopefully I can get it figured out.

  10. #9
    Dirtywaterdiver's Avatar
    Dirtywaterdiver is offline Cadillac Owners Fanatic
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    Re: Carb gasket differences

    That cross over on the intake is for warming up the carb during cold weather,
    or at least that was the thinking.

    It is not needed and you can get threaded plugs, tap it. and block the channel closed.

    You can also plug it off at the valley pan gasket using strips cut from an older pan gasket

    Have you also got the metal base shim?

    Have you tried spraying carb cleaner around the base to see if it stalls out?

    Check the intake with flat stock to see if it is not a tad warped.


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