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Did older Q-jets not have a ported vacuum? Are my HEI and carb compatible?

Discussion in 'The Garage' started by Okiemuddog, Jun 14, 2003.

  1. Okiemuddog

    Okiemuddog 1/2 ton status

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    Well, I am sure everyone is tired of my damn questions, hell I am even tired of them /forums/images/graemlins/rotfl.gif.

    I am have another one though, did some Q-Jets not have a ported vacuum? I have checked the three ports I have on my carb, the two on the front of the carb have a strong constant vacuum on them and the other is on the choke side of the carb and it has "0" even under accleration. It is possible that my carb was set up to run a constant vacuum dist and my HEI is set up to run Zero at idle? I have been searching the garage so that is the reason behind this question. I can't get it to idle down with the advance connected, but with it diconnected it idles correctly. I am sure that the timing is correct with the advance disconnected, but with it hooked up it advances about 30 degrees at idle. Can anyone help me out? /forums/images/graemlins/thinking.gif

    Thanks in advance.

    Krennen
     
  2. bigblock44k5

    bigblock44k5 1/2 ton status

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    Re: Did older Q-jets not have a ported vacuum? Are my HEI and carb compatib

    as far as i know they all have ported vacuum. mine did from '71. just make sure you check all the ports with a vacuum guage. it has to have zero at idle and go up as you give it gas. i think its the port on the passenger side towards the front.
     
  3. pilgrim

    pilgrim 1/2 ton status

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    Re: Did older Q-jets not have a ported vacuum? Are my HEI and carb compatib

    the directions for my new eledbrook Q-jet show the distributor port, to be on the drivers side just above the very bottom one. which is for the canister vac switch.. the one on the passenger side is for the egr. i tested both of these with a vac guage mounted in the cab. if i remember the egr one had NO vac at idle and the drivers side had like 3-5" of vac. which leads me to belive that the drivers side is correct because they ask you to take off the vac advance to do the timeing which would be of no concern if there was no vac on it at idle like the egr port...

    both jump to 15-22" of vac with light pedal and steadly drop to no vac(almost) under moderate to heavy pedal force... this /forums/images/graemlins/confused.gif me because i thought that once the vac advance came in, it stayed in???? maybe the mechanical advance is supposed to take over /forums/images/graemlins/confused.gif than....
     
  4. bigblock44k5

    bigblock44k5 1/2 ton status

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    Re: Did older Q-jets not have a ported vacuum? Are my HEI and carb compatib

    ive never actually seen a distributer vacuum source that had any vacuum at an idle. unless the idle was too high...
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Check the port at idle and slowly increase idle while watching a gauge.

    The "ported" vacuum for EGR and vac advance is a small slot in the primary side venturi, so with the throttle not in the right "region", it *will* read 0.

    Vac advance is for cruise, so if setup for ported vacuum, the slot will only be "actve" during cruise.
     

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