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Thread: Rochester 4GC

  1. #1
    Join Date
    Aug 2006
    Location
    Belgium
    Posts
    4

    Default Rochester 4GC

    Hello, I'm new to this forum and hope someone can help me with my problem.

    I'm in the middle of restoring a Range Rover Classic. The car has a 3.5 litre V8 (215ci). As you probably know Landrover bought the rights to build the aluminium V8 from GM. I wasn't satisfied with the twin Zenith/Stromberg carburetors, orginally mounted on the Range Rover. That's why I bought the Rochester 4GC. This kind of carburetor was also installed on the original Buick 215 ci V8, correct me if I'm wrong.

    I bought the carburetor from a member of the local Landrover club. The carburetor should have been mounted on a Buick 215 ci, but I'm not quite sure because the ID-tag is missing. Also there is no cast carb number stamped on the side. The only thing I can tell about the carburetor is that it has wedge type floats with dimples.

    The Rochester 4GC has been completely rebuild using a carburetor overhaul kit (#DAT 125) which I bought from the guys from classic buicks.

    CONNECTION PROBLEMS

    I have some questions concerning the connection of the carburetor.

    Choke system:

    As you know the Rochester 4GC has an automatic choke. The choke system is composed of a thermostatic coil, vacuum piston, offset choke valve and fast idle cam. Its operation is controlled by a combination of intake manifold vacuum the offset choke valve atmos*pheric temperature, and exhaust manifold heat.

    After dismantling the choke housing assembly I discovered that the choke baffle plate was damaged. Can I still get this kind of baffle plate?

    As the engine warms up, hot air from the exhaust manifold is drawn into the thermostatic coil housing. The hose that connects the exhaust manifold to the carburetor choke housing assembly is missing. Can you tell me how the choke housing is connected to the exhaust manifold?

    Is it also possible to get a manual choke for the Rochester 4GC?

    Vacuum connections:

    The most difficult part is the connection of the vacuum ports. In picture 1a you can see the carburetor mounted on the intake manifold. The red arrow in picture 1b shows a constant vacuum port which is situated at the secondary side of the carburetor. I presume this vacuum port is connected to the brake system? Is this correct? As my car is a 4x4 I will need another constant vacuum port for the Diff lock. I can drill a hole in the intake manifold and connect the hose for the diff lock to this vacuum port.

    After inspecting the throttle body assembly I discovered another vacuum port which is located at the primary side or pump plunger side of the carburetor. You can see this vacuum port in picture 2 indicated by a red arrow. I presume this is the idle speed air adjustment port. Should this be blanked or must it be kept open?

    Timed vacuum port:

    This item is beginning to give me nightmares.

    In my car (Range Rover) the distributor has a vacuum connection. This vacuum connection on the distributor is connected to a timed vacuum port which is located on the original Zenith/Stromberg carburetor.

    When I studied the Rochester 4GC I could not find a timed vacuum port. Can you tell me where (on the Rochester 4GC) I must connect the hose of the vacuum connection of the distributor. In stead of using the original distributor I will get a Mallory dual point or unilite distributor but these also have vacuum connections. So the problem remains....


    I know this this is quite a lot of information. But I hope you can help me sort things out.

    Yves
    Attached Images Attached Images

  2. #2
    Join Date
    Dec 2005
    Location
    Minnesota
    Posts
    400

    Default

    I've never used the Q-jet. That's what this is right? Does anybody know a good online resource for Rochester carbs? I'll do some looking too... Actually carbs in general...
    Nic '73 Vega GT Aluminum Wildcat 355
    http://www.cardomain.com/ride/2357894

  3. #3
    Join Date
    Aug 2006
    Location
    Belgium
    Posts
    4

    Default

    The carburetor is a Rochester 4GC, which is easily recognised by the vents on the air horn. This was the first four barrel design by Rochester.

 

 

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