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Thread: How can I properly use a 70-75 quadrajet on a 68?

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    FoxRodder's Avatar
    FoxRodder is offline Cadillac Owners Fanatic
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    How can I properly use a 70-75 quadrajet on a 68?

    Bought a used rebuilt carb from another member to replace the misbehaving one on my 68. Problem is it decodes to be a 72 model. So now, wondering if there is a good solution to make it work correctly because the bases, manifolds, and gaskets are different. The 68 has heat passages and a specific gasket that connects to them. It then has a heat shield/shim that goes between the gasket and the carb base. The 70 up models do not appear to have heat passages from the manifold or the steel shim. Anyone know what my options are? So far all I can think is to put the 70-75 gasket with no shim and hope I get no problems from the heat passage, or to use the 68 gasket, steel shim, and then the 70 up gasket on top of the shim. I am in Florida so it never gets all that cold here to worry about heating the base of the carb.






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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: How can I properly use a 70-75 quadrajet on a 68?

    It is not always a good idea to mix systems. Do the two carbs share the same choke systems? I believe the '68 uses a divorced choke, and by 1974 they were using electric choike systems. I would explore exchanging the carb base plates, because that carb will not mate to the '68 manifold, without causing problems.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: How can I properly use a 70-75 quadrajet on a 68?

    Find the HP Publications book on Quadrajets by Doug Roe. Everything you ever want to know about Rochester and QJ. Google or eBay. "rochester quadrajet doug roe".

    More electrical and electronic stuff in the mid-70's QJ's. You can get an electric choke kit for the '68.

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    FoxRodder's Avatar
    FoxRodder is offline Cadillac Owners Fanatic
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    Re: How can I properly use a 70-75 quadrajet on a 68?

    This one still has a divorced choke. Seller had it on his 68. Waiting to hear his way of making it work. Just thought I'd see if anyone else might have gone through it.


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