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vacuum gauge needle vibrates 1"HG

Discussion in 'The Hokey Ass Message Board' started by Von Rigg Fink, May 29, 2008.

  1. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    not new engine but new heads new cam. dont know if its a new problem , first time on the vac gauge..all the readings that would indicate lower end problems are non existant. im on the phone with comp cams right now to see if the valve over lap sequencing is a possibility
     
    spanners likes this.
  2. mac762
    Joined: Jun 28, 2007
    Posts: 676

    mac762
    Member

    This is probably the best answer for what you're seeing. I went to a braided line on my oil pressure gauge and it was a bigger dia than the factory line. I had read that it might make the gauge flutter a bit and it does. But I don't worry about it.
     
  3. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage


    definetly not grasping at straws..i Will find out what is causing both issues.
     
  4. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    comp cams says the valve overlap isnt big enough on this cam to create that type of reading..
    i do have a machine grade vac gauge..that could be the issue..
    my automotive designed gauge will be in this weekend (i hope)
    im going to stop speculating..i was hoping someone would come on here and say " I had the exact same shit" " and "this is what i found to be the problem"
    but that guy might end up being me..;)
    im going to get to work on it this weekend. if i do solve it..I'll post it.:cool:

    wouldnt that be a real pisser if it was the dam gauge all this time?
     
    Dan Timberlake likes this.
  5. I don't know about vacuum but I have had pressure gauges fluctuate in the past and cured the problem by using a snubber. I have a couple of them in the parts drawer at home that I have saved for years in case the problem ever crops up again. I had an erratic oil pressure gauge in a car several years back and the snubber cured the problem at the gauge. The ones I have are set up for aircraft AN style fittings but I have seen them with compression fittings and tapered pipe too.
     
  6. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    CB Chief..show me this "snubber"..can you?..what is its real or tech. name?
     
  7. T-Roy
    Joined: Aug 12, 2006
    Posts: 931

    T-Roy
    Member

    Good thread. The vacuum gauge on my motor is doing the same thing. Rebuilt heads, new cam, lifters, springs etc. I still need to rule out a hot valve adjustment though.
     
  8. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    Ok a bit of an up date as to what i did tonight. New plugs gaped at 0.045 ..and it did wake up the engine alot. (originally i had em at .032
    my mistake) timing was a little off. the new spread bore carb base gasket and spacer helped a but too. need to get it out on the road for "feel" and "listen" test. but it already sounds more alive.
    friken gauge still does the shakey jake shit, im starting to think its the dam gauge. If the weather clears up i will go out and make some full throttle dead starts and see how it feels off the line. than make a highway run to see if the stumble is gone.
    sounds like michigan might get hit with some shitty weather for the next few days , so we'll see.
     
  9. nexxussian
    Joined: Mar 14, 2007
    Posts: 3,240

    nexxussian
    Member


    Ah-yup.
     
  10. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    Ok here is what i did..changed the Carb Base gasket and 1 inch spacer to the correct one for a spread bore carb on a dual plane intake..that helped the low end torque and smoothed the engine mis a bit. Also changed the spark plugs to AC R44TS. and Gap to .045 and that really woke up the engine smoother acceleration. Engine runs pretty dam good. as for the vac gauge..still has the high frequency needle fluxuation. Im thinking the Gauge is the culprit. Getting a new one hopefully this week so I will see. oher than that engine seems to run just fine.
     
  11. 7&7
    Joined: Jan 6, 2006
    Posts: 362

    7&7
    Member
    from Colorado

    I believe it is the guage as well. You can get a snubber at your local HVAC supply houses. Yes their full intent is to smooth out eratic guages and help with pressure flux. Normally used on pumps and other equip. that have pressure surge. 14-15 in. of vac would be heaven my little small block has 4.5 to 5. Now thats a cam. I had to pull the power valve assemblies out of my 2GC's to cure some of my problems. Hope you figure it out good luck.. Have you checked your coil/charging system?
     
  12. Quiz the cat that machined your heads. See if the valve spring seat pressure is high enough for the hot street cam. I have seen this make a shaky needle at idle. I see you went to a wide gap plug and that's good,can't just bend the narrow gaps out as the electrode and the tip need to run evenly spaced. I recall a rant awhile back on something about Accel Plugs????>>>>.
     
  13. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,418

    Von Rigg Fink
    Member
    from Garage

    well I could have re-gaped the Accel's (maybe) but i had and like AC plugs so I gaped them at what i read to be factory specs .045. I still have and will keep the Accels around JIC.
    when i get the new Vac. Gauge I will see if it makes any difference. Things have seemed alot easier to tune and tweek since the addition of the correct Carb Base Spacer and gaskets, and the wider gap.
     
  14. KenC106
    Joined: Sep 21, 2023
    Posts: 3

    KenC106

    I know this is old but I worked this out after googling for 6 months, this may not be your issue but posting for someone this applies to:

    dual plane intake manifold, no gap, vacuum gauge vibration like crazy

    cause: the front two vacuum lines seem to be slightly isolated and at minimum some resistance to one port. If you flip over the Holley you’ll notice that the machined channel on the secondary’s is machine to both with a wide, connection of your gauge to the power steering line you’ll get a steady reading.

    you could also add a 1/2” open carb spacer but defeats the dual plane manifold you purchased it for in the first place.

    Hope this helps someone

    update: I capped off the front two vacuum ports, then did power brakes off the manifold, and pcv off rear vacuum port. Works perfectly. I also put in a plugged 1/8 vacuum line off the pcv, when I need to check vacuum with a gauge I’ll plug the pcv and plug into the 1/8 tap on that line
     
    Last edited: Oct 13, 2023

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