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Carb experts - Quad..I am not getting any vacuum on (see pic)

Discussion in 'The Garage' started by jakeslim, May 4, 2003.

  1. jakeslim

    jakeslim 1/2 ton status

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    OK, I thought it was a bad torgue converter(you may have seen my earlier post), but it turned out to be ZERO vacuum from carb on designated vacuum advance connection for distributor!! I checked the vacuum on the other ports on carb and they were fine, so I moved distributor to a vacuum connection on passenger side of carb and am now getting an 18 on my vacuum quage. Why am I getting Zero vacuum from this connection? It is the bottom black capped connection in Pic...right below the factory blocked port. Was this the wrong port to plug the distributor in?

    [​IMG]
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Install the vacuum gauge on that fitting.

    Start the truck and increase engine RPM's slowly. Guessing you'll see vacuum come in once you start coming off of idle.

    Try the same thing to the one above it and to the right, as that could be vac advance as well. *Usually* the fittings are different sizes so you can't easily fit the wrong size hose on it (without stretching the rubber a lot), so the fitting on the advance cannister should be the EXACT same size as the fitting on the carb that it was destined for.

    IIRC, EGR will be "timed" vacuum on the passenger side, and vac advance is "timed" on the drivers side. The later carbs I'm not too sure how many timed ports could be present, and even the fitting sizes could have changed, since one fitting sometimes t'd into multiple hoses, might be connected to a swtich, etc.
     
  3. sled_dog

    sled_dog 1 ton status

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    I have almost zero vaccum at idle on my vaccum advance. My dad's race car has more vaccum than my truck. BUt when I get on it I have way more vaccum than he does. Don't as me why they are hooked the same spot, both qjets. Just his is an Olds 350 and mine is a Chevy.
     
  4. jakeslim

    jakeslim 1/2 ton status

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    It is a new Edelbrock quad. I checked all the ports on it and found one with the necessary vacuum. When I checked the one in question, I had zero reading at idle. The one just above it read a "5" at idle. It seems to run much better now when I test drove it. Do you think I should move the vacuum advance back to front of carb? I have no EGR
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Try it both ways. Vacuum advance is an emissions control/economy device (only working under high vacuum conditions) and GM typically (probably 95% of all applications) went with ported (non-manifold) vacuum on their carbed vehicles.

    A lot of it depends on engine, but the only real difference is how much vacuum you are pulling at idle, which means how much vac advance you are running at idle. At cruise it will be the same ported or manifold vacuum, since the ported slot will be open then, and ported/manifold vacuum is the same thing, just one isn't "constant".

    Obviously, on ported vacuum, you will see 0 vac advance at idle. (although a little might "slip" by)
     

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