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Thread: eratic vacuum
          
   
   

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  1. #1
    Dean C. is offline CHR Member Visit my Photo Gallery
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    eratic vacuum

     



    Hi all, i did my valves over again, this time at a 1/2 turn 1/4 turn seemed to loose, but when i hook up a vacuum gauge on my carbs ( full vacuum) the reading is bouncing between 14-18 and engine stumbles. Any suggestions?

  2. #2
    nitrowarrior's Avatar
    nitrowarrior is offline CHR Member Visit my Photo Gallery
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    What cam do you have? From your last thread we never got that info. It could be useful to know that for diagnosing the problem.
    Last edited by nitrowarrior; 10-15-2007 at 04:09 PM.
    What if the "Hokey Pokey" is what it's really all about?

  3. #3
    Dean C. is offline CHR Member Visit my Photo Gallery
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    mild 204/214 edelbrock 420 lift

  4. #4
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    have you checked for a vacuum leak?
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  5. #5
    Dean C. is offline CHR Member Visit my Photo Gallery
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    yea no vacuum leaks, the needle is a little bouncy and goes from 14 -18 and the idel is not to steady motor has slight stumble, i think i still hear some clacking faintly from the valves could i need to go more than the 1/2 turn?

  6. #6
    nitrowarrior's Avatar
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    If you're running stock steel rockers, you may have wear causing the tip of the rocker to not contact the valve stem squarely causing a light click. Some roller rockers have a tendency to make a bit of ticking noise. What are you running for rockers?
    What if the "Hokey Pokey" is what it's really all about?

  7. #7
    Dean C. is offline CHR Member Visit my Photo Gallery
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    stamped steel, this is my first time adjusting valves, i folowed the procedure to the letter, i would have thought they were perfect but now when its running i can hear them clattr slightly, and i don't get the vacuum reading.

  8. #8
    Dean C. is offline CHR Member Visit my Photo Gallery
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    if i bring the rpm up to 1500 -1800 then the motor smoothes out, (not sure of the vacuum reading at that rpm)

  9. #9
    nitrowarrior's Avatar
    nitrowarrior is offline CHR Member Visit my Photo Gallery
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    If tere is even a slight bit of wear between the rocker tip and/or the valve stem tip, you will get some slight ticking. Tightening the valves won't make it go away just make the run condition worse. As far as the vacuum surge, one quick check is to take your hand while the engine is running and slight lower it over the primary side of the carb and creat a choke style condition. Raise and lower your hand to restrict the air flow ever so slightly and watch the vacuum gauge. A lean idle circuit can cause this stumble and fluctuating vacuum reading.
    What if the "Hokey Pokey" is what it's really all about?

  10. #10
    Dean C. is offline CHR Member Visit my Photo Gallery
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    so by using your hand when you place it over the primarys the vacuum should fall and return when you remove you r hand ? if this happens the problem is whith the idel mixture?

  11. #11
    nitrowarrior's Avatar
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    Most likely. The idle circuits in all carbs are a big part of part throttle to 1800-2000 rpm range. Give it a check.
    What if the "Hokey Pokey" is what it's really all about?

  12. #12
    Dean C. is offline CHR Member Visit my Photo Gallery
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    Thanks, iv'e had enough of this car for one night but tomorow it will be the first thing i do.. thanks again for your help..

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