1972 472 quadrajet 4mv carb issues
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500, 472, 425, 368 Discussion, 1972 472 quadrajet 4mv carb issues in Cadillac Engine Technical Discussion; i just did a carb rebuild and after putting the carb back on the car it still "cuts off" when ...
  1. #1
    billsif is offline Cadillac Owners Member
    Automobile(s): 1972 Sedan Deville
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    1972 472 quadrajet 4mv carb issues

    i just did a carb rebuild and after putting the carb back on the car it still "cuts off" when i floor the gad pedal, and the secondaries dont seem to be opening. should the secondaries ever open in park while revving the engine? also, when i turned off the engine after some revving i noticed a lot of white plumes of misty smoke rising out of the intake manifold fron underneath the choke coil i think it is... (the coil that has it's own separate housing mounted next to the carb and with linkage attaching it to the carb).

    i guess my questions are:

    1. what is this white smoke coming out of the manifold beneath the choke coil, and is it normal?
    2. why does my engine "hesitate" or "cut out" or "get quiet" whatever you wanna call it when i floor the gas pedal?
    3. should the secondaries ever open when the car is in park in my driveway, and if so under what conditions?

    thank you very much.. your replies will help me get this 472 running smoothly again. : )

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  3. #2
    davesdeville's Avatar
    davesdeville is offline Banned
    Automobile(s): 1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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    Re: 1972 472 quadrajet 4mv carb issues

    1. The white mist is fuel/air mix, I'd think. If it is, that's very dangerous and could cause an engine fire pretty easily. Don't drive the car until this is fixed!

    2. Dunno. Did you replace the accelerator pump when you rebuilt it?

    3. The secondaries should open if you rev it high enough. I had basically the same carb on my 425 and I could get them open. And you have almost 50 more cubic inches to work with.

  4. #3
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 1972 472 quadrajet 4mv carb issues

    I don't know anything about them myself but the book Rochester Carburetors: Tune, Rebuild or Modify by Doug Roe is supposed to be THE book to have when you want to learn about Q-Jets.

  5. #4
    DaveSmed's Avatar
    DaveSmed is offline Cadillac Owners Connoisseur
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    Re: 1972 472 quadrajet 4mv carb issues

    The white smoke could be anything. I would think that you would smell it if it was air/fuel, and that it would be sucking air in with the vacuum anyway. If you recently washed your engine, it could be steam. When your driving, see if the car feels responsive up until you notice a change in throttle pressure (with the car fully warmed up, choke off). If so, I would be inclined to believe that you are afflicted with "Quadra-bog". This is caused by the rate that the secondaries open at. as soon as you hit a certain spot in the throttle, the larger butterflys start to open (provided there not locked out via choke). The vacuum pulls the flaps on top of the carb open, and the valves allow fuel to flow into the secondaries. The problem arises when the valves snap open too quickly. Say you punch it, the butterflys open all the way, and the valves fly open. due to the low vacuum signal, and the sudden opening, the fuel can't get there in time to prevent a sudden lean condition. There are devices on the carb to cushion the opening, but for whatever reason, they tend to not work as well over time. Ususally someone disconnects them for whatever reason (the little dashpot on the front passenger side of the carb is one. at strong vacuum, those valves will not open, only on acceleration) This also could prevent it from opening at idle, since the engine is not under load, it may have too much vacuum to unlock that dashpot. Hope this clears some of your questions up.

  6. #5
    davesdeville's Avatar
    davesdeville is offline Banned
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    Re: 1972 472 quadrajet 4mv carb issues

    White misty smoke sounds alot like air/fuel. It could be steam, but I wouldn't think the top of the intake manifold would get hot enough to make steam.

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