Idle Tuning Troubles

Discussion in 'Troubleshooting & Diagnosis' started by notstock78, Mar 23, 2021.

  1. notstock78

    notstock78 Member Lifetime Gold Member

    Messages:
    99
    Likes Received:
    0
    Joined:
    Feb 19, 2010
    Location:
    Sioux Falls, SD
    Hey Everyone,
    I am trying to tune my SBC 410 and having some idle problems. It is running rich at idle.
    I have the initial timing set to 15 degrees.
    I am running a Holley street avenger 770.
    I have a power valve block off plug in it just to rule out the power valve leaking.
    The idle mixtures will only respond when they are all 4 all the way in it will kill the motor. The motor will run with only one of them out about 1/4 of a turn. Is this normal or am I getting fuel from somewhere else?

    Any ideas where I could be getting fuel from?
     
  2. flybye70ss

    flybye70ss Veteran Member

    Messages:
    923
    Likes Received:
    57
    Joined:
    Dec 6, 2002
    Location:
    Allen, TX
    do you have the idle butterflies open enough exposing the transfer slot?
     
  3. carhead22000

    carhead22000 oldblue

    Messages:
    647
    Likes Received:
    274
    Joined:
    Sep 5, 2011
    Location:
    canada
    sounds like it might be a vacuum leak....first off set all air mixture screws to factory setting.set your timing by ear for now.. twist it till you have the highest idle,then drop it back just till you hear it drop.nex,get a propane tourch turn it on no flame just gas.go around base of carb and intake while running.if you come across your leak your engine should rev up from the propane.hope this helps you out....keep us posted.
     
    mrluckies likes this.
  4. notstock78

    notstock78 Member Lifetime Gold Member

    Messages:
    99
    Likes Received:
    0
    Joined:
    Feb 19, 2010
    Location:
    Sioux Falls, SD
    Great!

    I do have the transfer slots just barely exposed.

    I will check for a vacuum leak.

    Thanks for the ideas. I will let you know what I find.
     
  5. G72Zed

    G72Zed Veteran Member

    Messages:
    3,059
    Likes Received:
    1,526
    Joined:
    Sep 8, 2015
    Location:
    Canada
    I would try and run as much initial timing as possible, 22-24* if you can.

    It could have an internal leak in the PV cavity/main body, or the transition slots are oversized from the factory.

    i have also seen incorrectly drilled IFS and IAB that played havoc with certain carb lines.
     
  6. djorgensen3

    djorgensen3 Veteran Member

    Messages:
    796
    Likes Received:
    168
    Joined:
    Oct 15, 2009
    Location:
    Peoria, Az
    Set the primaries at .020"-.040" open with idle screw and then don't touch it. Set idle mixture screws to 1 1/4 turns open. Open the secondaries to let in enough air to set idle to acceptable rpm. Then you can go back to primary idle screw to fine tune. You'll also be able to fine tune the mixture screws. Make sure timing is right. Try it 18⁰ initial with 18⁰or so mechanical. Limit manifold vacuum advance to 8⁰ or so. See where you end up with these settings. You may have to change idle air bleeds if this doesn't help. I'd also pay attention to what G72Zed says. He gives out good advice.
     
  7. carhead22000

    carhead22000 oldblue

    Messages:
    647
    Likes Received:
    274
    Joined:
    Sep 5, 2011
    Location:
    canada
    was also thinking check the pump shot on carb make sure it is working....and if you flooded the car....i dont care if only once,change plugs.dont makem like they used too.
     
  8. notstock78

    notstock78 Member Lifetime Gold Member

    Messages:
    99
    Likes Received:
    0
    Joined:
    Feb 19, 2010
    Location:
    Sioux Falls, SD
    I got this figured out. I did 2 different things. One, added a fuel pressure regulator and set it to 6.5 PSI. It was at 7.5 without the regulator. The other thing was to put more initial timing in it. I bumped it up to about 19 and it finally responds to the idle mixture screws. Thanks for the help everyone!!
     

Share This Page