vacuum secondaries won't open

Discussion in 'Engine Topic' started by nick71RS, Jan 29, 2005.

  1. nick71RS

    nick71RS Member

    46
    0
    Nov 25, 2002
    california
    holley 3310 on perf rpm air-gap
    406 10.2:1
    solid roller 240/248 @ 0.050
    zz430 (fastburn) heads, right springs for cam
    5.7 rods, HEI/MSD module
    long tube headers/H-pipe/dual exh
    4spd muncie
    etc.

    problem is the vac secondaries NEVER open. I was suspicious so used the paperclip trick (paperclip on the little rod from the vacuum diaphragm) which would easily be pushed down the rod as they open.. it never moves.

    I put the lightest spring in it, still never opened.

    took the vac. secondary pot off, put vacuum on passage to carb body and the passage to both the primary and secondary side is clear and flows air.

    put vacuum to the vac diaphragm assembly, it pulled the rod in just like it's supposed to and held vacuum, pull on the rod was very strong.

    put the vac diaphragm assembly back onto the carb with a new cork gasket for the vacuum passage, and the vac secondaries still don't open AT ALL.

    the linkage from the primary side to the secondary side is in good shape, hasn't been hacked or modified or anythying. Ssecondaries can be manually opened if the primary side is held open. carb gets full throttle from pedal, so throttle cable is ok.

    check ball is in the vac secondary pod where it belongs per holley info.

    test method is 2nd gear to at least 5500rpm due to inability to maintain any traction in 1st.

    otherwise, motor runs great, sounds great, awesome torque, just quits pulling any harder around 3500 due to (presumed) lack of airflow. it doesn't seem to build any more horsepower once past around 3000 or so because of the carb. i'm sure the engine needs more air - the response to the throttle is VERY crisp, even the slightest amount of letting off and you feel a power loss, so it's not like the motor is lame and doesn't need anymore air. it never bogs or stumbles or acts like it has any kind of fuel delivery problem.

    help?

    ------------------
    '71 RS 406 4spd


    [This message has been edited by nick71RS (edited January 29, 2005).]
     
  2. Jim Mac

    Jim Mac Veteran Member

    2,196
    0
    Dec 28, 2004
    tucson az USA
    I never heard of the paper clip trick but how about putting a small machine screw and nut in the secondary linkage to make it a mechanical secondary, I know the 3310 doesn't have an accelarator pump on the secondary but for this test just ease into the throttle till you get above where you were'nt making power and see if it changes. if you aren't finding a difference I'd check the advance on your HEI. Jim
     
  3. Mwilson

    Mwilson Veteran Member

    with the canister off can you push the rod in then plug the hole with your finger let go of the rod and it stays in?
     
  4. Air_Adam

    Air_Adam Veteran Member

    Heres a better idea... istead of trying to convert it to mechanical linkage for a simple test, disconnect the linkage to the secondaries and see how it acts. If its the same, then your secondaries really aren't opening.
     
  5. Mwilson

    Mwilson Veteran Member

    make sure to leave the linkage rod on though take the c clip off at the canister side only because if they do open and that linkage rods off they wont close ! I lost a brand new motor and gained 10 stitches when i removewd the linkage rod in my shop and the car was idling i reved it to 2000 and bumped th secondaries on accident with my hand the motor sucked em open and went stait to 7500 until it blew! a belt flew off in peices and split my head open i was to dazed to shut it off in time
     
  6. nick71RS

    nick71RS Member

    46
    0
    Nov 25, 2002
    california
    See picture for "paper clip trick". it's in one of holley's tech guides on their web site. the paper clip moves easily on the rod with the slightest bit of pressure. If the rod is pulled up into the diaphragm housing, the paperclip gets pushed down the rod. so, how far down the rod the paperclip is, is how far they opened. my paperclip doesn't move.

    Timing is 20* initial (as demanded by the cam for low-rpm drivability) and 34* total (fastburn heads work best at 32-34*). mechanical doesn't start coming in to around 1300rpm and is all in @ 3300. all verified and re-verified with timing light after custom distributor work/curve work. idles at 1000. front carb blades have small hole drilled in each to acheive proper idle with transfer slots covered the right amount.

    I didn't specifically check the vac diaphraghm by pushing the rod in and holding thumb over the hole, but i did check it with a vacuum pump. it held any level of vacuum and any rod postion (partial or full vacuum) for an indefinate period of time. If this isn't a valid test I can certainly pull it off and try the thumb method..

    I am 100% positive the secondaries aren't opening. have played with the carb extensively and theres no way the secondaries can open without moving the paperclip, and there's no way they can close and move the clip back up against the bottom of the vac pod/canister. And the paperclip certainly isn't tight enough to prevent it from moving - it took very little vacuum to start pulling the rod in and move the paperclip with the pod off the carb. heck, with vacuum on the diaphragm i coudn't even pull the rod out by hand, it seems to have good pull under vacuum.

    [​IMG]

    [This message has been edited by nick71RS (edited January 29, 2005).]

    [This message has been edited by nick71RS (edited January 29, 2005).]
     
  7. nick71RS

    nick71RS Member

    46
    0
    Nov 25, 2002
    california
  8. Rick WI

    Rick WI Veteran Member

    10,408
    0
    Jul 9, 2001
    Madison, WI
    You used the yellow spring?
     
  9. Jim Mac

    Jim Mac Veteran Member

    2,196
    0
    Dec 28, 2004
    tucson az USA
    I've never seen that paper clip trick I learned something new, thanks! Jim
     
  10. Mwilson

    Mwilson Veteran Member

    man im stumped doesn't make sense!
    i bought a new holley one time and the vac passage wasn't drilled but you've already verified that too?
     

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