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Q-jet vacuum

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Mastiff, Aug 5, 2003.

  1. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I did search on this, but couldn't find quite what I'm after.

    On the manifold behind my carb I have a little thing screwed in that has two vacuum lines coming off, one for the vac advance and one for the transmission. I'm not sure if this is a direct line to the manifold vacuum or if it's switched somehow, anyone know?

    If it's a straight shot to manifold vacuum, can I get rid of this thing and connect the lines directly to the carb somehow? The fact that I have this may be a carry over from when I had a spaghetti of 50 million vacuum lines for all the emissions stuff. Now I just have the EGR.
     
  2. Dunc03

    Dunc03 1/2 ton status

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    If the vacuum connector is an aluminum T that screws into the manifold, it should not be switched, it should be a direct manifold vacuum source. It is a direct source on my 86. I don't think getting rid of that vacuum source will really benefit you. If this source is hooked directly to the vacuum advance you would have advance at idle when you are not supposed to. There should be no vacuum advance at Idle. But if it running fine then I guys its hooked up Right. Hope that helps in some way.
     
  3. Mastiff

    Mastiff 1/2 ton status Premium Member

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    The reason I'd want to lose it is because it's very close to the vacuum break on the back of the Q-jet and there's kind of a cluster of vacuum lines back there that have to make some abrupt bends to clear stuff. Seems stupid when the Q-jet is full of unused vacuum ports.

    I guess I can check the vacuum that's coming from that thing and see if it's direct manifold vacuum. I think I've removed it with the engine running before, to check the timing, and the engine didn't run down before I plugged it. Maybe that means it's switched somehow? I don't think the engine does real well with a hole in the manifold?

    It's running fine, but why would it be bad to have advance at idle? Isn't the idea to advance it when there is no load and then retard it under load to prevent ping?
     

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