Carb vacuum line routing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by HoustonK5, Oct 1, 2001.

  1. HoustonK5

    HoustonK5 Registered Member

    Aug 21, 2001
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    Houston, TX
    Had a heck of a time towing my boat without secondaries yesterday. The joker I bought the blazer from had so many hoses blocked up including the secondary vacuum connection.

    Where is a good source for a vacuum hose routing diagram? I have a haynes manual, and all it has is an expanded view of the actual carb, no hoses. I have an image located here: <a target="_blank" href=></a> The main help I need is number '1' in the picture...The secondary vacuum at the top of the pic. Where does that route to? If you know where the other numbers go too, please let me know.

    Thanks for the help.

    81 K5
  2. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
    Likes Received:
    Grand Rapids area
    I thought that all Quadrajets had mechanical secondaries. Am I in for more education today?

    Ah yes, that image cleary shows the mechanical seconday linkage. The throttle butterflies will open based on the throttle position and the top flappers (whatever those huge things are called) will open based on demand and adjust the position of the secondary metering rods in the secondary jets with them.

    #1 is the rear vacuum break. It is just a little vacuum motor that adjusts the position of the choke plate based on engine load when the choke is operating (it richens the mixture even more when there is heavy load on a cold engine). The choke spring wants to keep the choke plate virtally closed, but this gizmo prevents that by a little bit, except for when you mash the gas. Then the vacuum to it is reduced and the choke is allowed to close further.

    The vacuum line to #1 goes to a small nipple sticking out of the rear center of the carb, just like is shown in the picture. There should be only one such fitting on the back.

    If you do a search, someone posted a picture of their hose routing diagram before.

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