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Thread: Air Cleaner Snorkel

  1. #1
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    Air Cleaner Snorkel

    My '76 Chevy is equipted with Rochester 4 BBL Quadrajet Carb. There is a damper in the air cleaner snorkel which controls fresh air while the car is in motion and warm air from the exhaust manifold entering the carb while the engine is warming up. According to a repair manual, this damper should open when the engine is first started cold (like first thing in the morning). But the problem is the damper is ALWAYS open and try as I may, I couldn't close it by hand .Anyone know the reason why?

  2. #2
    Ridin Dirty dom's Avatar
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    I think it was called a heat riser or something like that.

    Anyhow, I'm seen them with mechanical linkage.

    Guess maybe you have that.

    Being that you're in Hawaii I'd bet someone jammed it open because it never gets cold enough there for such a device.

    Dunno for sure though.

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    Senior Member grouch's Avatar
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    Quote Originally Posted by ChevyMan View Post
    My '76 Chevy is equipted with Rochester 4 BBL Quadrajet Carb. There is a damper in the air cleaner snorkel which controls fresh air while the car is in motion and warm air from the exhaust manifold entering the carb while the engine is warming up. According to a repair manual, this damper should open when the engine is first started cold (like first thing in the morning). But the problem is the damper is ALWAYS open and try as I may, I couldn't close it by hand .Anyone know the reason why?


    Is the vacuum hose from the carburetor attached? I think yours is vacuum controlled. Earlier ones were a thermoactive spring. If you have a stock carburetor, there will be a vacuum hose from the carburetor body to the air cleaner housing, then another one to the flapper assembly.
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    There is a metal tube running from the exhaust manifold up into the snorkel bottom to direct warm air during the initial warm-up period and it's called the Heat Stove. The Heat Risers were used in earlier cars like my 1952 Chevy.

  5. #5
    Senior Member grouch's Avatar
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    Quote Originally Posted by ChevyMan View Post
    There is a metal tube running from the exhaust manifold up into the snorkel bottom to direct warm air during the initial warm-up period and it's called the Heat Stove. The Heat Risers were used in earlier cars like my 1952 Chevy.

    That tube was used well into the 90's. The diverter valve opens to draw air up it. It's been warmed by the exhaust manifold so the pressure drop in the carburetor body does cause ice build up from the pressure drop. I've seen engines stall from ice clogging the venturi area but mechanics couldn't find the problem as the ice would melt as soon as the engine sat.
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    Senior Member BrentP's Avatar
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    I've attached a page from "Automotive Engines" by Crouse, 1971. It shows how the system works. Bimetal spring acts as a vacuum switch. The application of vacuum changes the position of the damper.
    Attached Images Attached Images

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    Brent, I have couple of books showing similar illustrations as shown in your reply. I believe during all these years ( 35), no one service the snorkel assembly. Perhaps I could replace the sensor in the air cleaner to enable the damper to operate the way it should. I can reach it by hand from the front end of the snorkel and notice it stuck in the "open" position. Push it close and it snaps open by itself , preventing warm air from the manifold to enter the air cleaner during the warming up period when I first start the car in the morning. It takes at least 4 minutes for the choke lever to fully open.

    I wonder if I'm able to obtain the correct parts for my air cleaner assembly?

  8. #8
    Senior Member grouch's Avatar
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    Quote Originally Posted by BrentP View Post
    I've attached a page from "Automotive Engines" by Crouse, 1971. It shows how the system works. Bimetal spring acts as a vacuum switch. The application of vacuum changes the position of the damper.

    The description is of a Ford system (bi-metal spring) but the illustration is of a GM design. If there is no vacuum to the servo, it won't work. Default is open.

    On an older Ford, like used in the late 60's, early 70's, the spring is short when cold and long when warm. This is what operates it. GM did it differently. Mopar used a similar system. If the vacuum line isn't hooked up, the system stays in the open position. I'd make sure the connection on the carburetor has vacuum. Then make sure the hoses are connected.
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    >> I'd make sure the connection on the carburetor has vacuum. Then make sure the hoses are connected.[/QUOTE]<<

    I suppose you're correct. I remember the shop once worked on my carburetor and they forgot to connect the metal heat stove from the manifold to the snorkel bottom. Perhaps the connections at the carburetor ends are disconnected. It's hard to notice unless you loosen and lift up the air cleaner assembly.

    I'll check that later. Thanks.

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