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Vacuum Advance Question 2

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by caryhenry, Jan 23, 2003.

  1. caryhenry

    caryhenry Registered Member

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    What is the vacuum advance supposed to connect to on an 85 305?
     
  2. wheelin_willy

    wheelin_willy Registered Member

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    vacumm advance on any car connects to the ported vacuum on the carb which means there is only vacumm upon acceleration.
    so bust out the vacumm cage and have fun
     
  3. caryhenry

    caryhenry Registered Member

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    where would the ported vauum be on an 85 305 with stock carb? (M4M carb)
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Most Q-jets ran ported vac from the drivers side front, but *usually* it will be one of the only ones that matches the hose size at the vacuum cannister. "Easy" to tell which is which, if it doesn't "suck" when you pull the hose with the engine idling, it's ported. There are usually two ported ports in the Q-jet, EGR and vac advance. EGR I believe uses a bigger hose than vac advance, and is on the passenger side typically.

    Too many variations in the Q-jets to say with certainty unless its' one year one application specific.

    Contrary to what some think, not all applications used ported vac advance, and to be honest, it doesn't really matter for its intended purpose..if vacuum is "high" its high, doesn't matter where its checked. Only difference is vac advance at idle, and SOME engines do like straight manifold vac advance.
     
  5. caryhenry

    caryhenry Registered Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Contrary to what some think, not all applications used ported vac advance, and to be honest, it doesn't really matter for its intended purpose..if vacuum is "high" its high, doesn't matter where its checked. Only difference is vac advance at idle, and SOME engines do like straight manifold vac advance.


    [/ QUOTE ]
    By this do you mean I can connect the vacuum advance to any open port with a good suction no matter if it's ported or not?
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    By this I mean in some applications GM used straight manifold vacuum. Of course, that was mostly in the late 60's early 70's, but depending on the engine, it might like manifold better than ported. I said that because it is not ALWAYS ported.

    Anyway, yours is a later vehicle, so it should be ported, but as was said, also "switched" through the TVS I believe. Thats an emissions deal, so if your truck engine vacuum harness has been hacked apart already, hookm it up to ported vacuum and you'll probably have no problems.
     
  7. wheelin_willy

    wheelin_willy Registered Member

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    it needs to be ported vacuum or gas mileage suffers /forums/images/graemlins/usaflag.gif
     

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