Constant vacuum or Zero at idle?

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

  1. Okiemuddog

    Okiemuddog 1/2 ton status

    Mar 3, 2003
    Likes Received:
    Guthrie, Oklahoma
    I got the timing set on my /forums/images/graemlins/k5.gif today and it is running a lot better, I have the timing set at 8 degrees BTDC, which I think is correct. My engine is out of an '81 K30. The problem I am having is that it idles about the correct RPM's with the vacuum advance unplugged from the carb. When you hook the vacuum advance back up the engine idles way up. I have checked to make sure that I have the correct port, but all the ports on my carb have vacuum at idle, I have a stock 4BBL Q-jet. Does anyone have any suggestions? Is my advance supposed to have Zero vacuum at idle or constant vacuum? If zero then where am I wrong with the advance causing the engine idle too high?

  2. bigblock44k5

    bigblock44k5 1/2 ton status

    Jun 8, 2003
    Likes Received:
    Hurlburt Field, FL
    the vacuum for the ignition is suppossed to be ported vacuum. it is suppossed to have 0 at idle and go up gradually as you give it gas. on a q jet i believe its in the front passenger side. check and make sure there is no vacuum at this port with it running.
  3. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
    Likes Received:
    Roy WA
    I believe some of the HD trucks were running un-ported vacuum well into the 80's, so that may be correct.

    Ported vac advance on a Q-jet will be on either the drivers or passengers side, but always along the front.

    You may see a little "leakage" even on the ported fittings, especially if you've got the idle screw cranked way in. more often than not though, it's the drivers side that has the ported vac for advance.

Share This Page