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Results 1 to 15 of 15
  1. #1
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default I was using my new vacuum gaug

    I was using my new vacuum gauge tester on carb and new advance timing light that indicates the RPM.

    I have a 1991 454CID.
    Is there any value to readings less then 700 RPM? Issue number 1 was that I can see very clearly that I was trying to idle at 600 RPM (out of gear). The vacuum was showing jerky movment that goes away as the idle increases. That looks like worn value guides from what I understand. At the 750 RPM the vacuum is at 17 and much more stable. However I see (and now with the clues hear) changes of 70 RPM up and down. I cannot get a soild idle. I think I need to tune carb more? Is there any value to sub 600 RPM out of gear? I having idle and sub 17 vacuum issues.

    I remember my manual said 600 RPM in gear and 600 to 750 is the idle

  2. #2
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,459

    Default Very low idle speeds are bad f

    Very low idle speeds are bad for your transmission gears. High idle speeds are bad for your transmission clutch. 6 to 650 in gear would be good.

  3. #3
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,531

    Default "You need to have a sound mech

    "You need to have a sound mechanical engine to get that carb dialed in. If the guides are worn, no point in doing anything else with the carb until the guides are fixed.

    How many hours are on the top end? both engines or only one?"

  4. #4
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default 1180. moving to second engine

    1180. moving to second engine this weekend

  5. #5
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,531

    Default "We used to see about 1000 hou

    "We used to see about 1000 hours as a service limit on a top end when I was in the shop. Looks like your about 20% beyond that so having worn guides and springs is very possible. Doesn't mean it is shot but it won't perform as well as if you freshened it up.

    When you raised the idle speed, did you check the mmain nozzles in the primaries to see if they "turned on"?"

  6. #6
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,320

    Default "That idle speed fluctuation c

    "That idle speed fluctuation could be a bad carb idle adjustment, bad plugs and or wires, incorrect timing, air leak, etc.

    I have a feeling you are over-analyzing the situation with your new toys! (Being brutal here, but honest.) If I were you I would eliminate all of the above BEFORE jumping to conclusions about worn valve guides. I've seen motors with many times that number of hours on them idle Rolls-Royce V-12 smooth.

    Jeff"

  7. #7
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default Re: First vacuum test on manifold newbie with some tools

    Jeff, never worry about being honest in you opinion.
    I will do more tests before anything. I didn't get time yet for compression.

    Interperting the vacuum test is new to me. It seemed jerky at idle and then smooth out at higher rpm. At 600 rpm vacuum jerks fast and surging back up and down by 70 rpm and vacuum 14.5 to 16.5. At 700-750 rpm vacuum better at 17. Vacuum jerks smooths out fast after 750 to 1000.

    If I bring my heads to a good shop I know, they do em for 600.
    Engine is tuned with new plugs.


  8. #8
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default Re: First vacuum test on manifold newbie with some tools

    Jeff, never worry about being honest in you opinion.
    I will do more tests before anything. I didn't get time yet for compression. Interperting the vacuum test is new to me. It seemed jerky at idle and then smooth out at higher rpm. At 600 rpm vacuum jerks fast and surging back up and down by 70 rpm and vacuum 14.5 to 16.5. At 700-750 rpm vacuum better at 17. Vacuum jerks smooths out fast after 750 to 1000.
    If I bring my heads to a good shop I know, they do em for 600.
    Engine is tuned with new plugs.



  9. #9
    Join Date
    Oct 2007
    Location
    , ny, us
    Posts
    835

    Default Re: First vacuum test on manifold newbie with some tools

    Although it is possible, it is unlikely that worn valve guides are the cause of this problem. Here is a link to how vacuum readings are interpreted.
    http://www.secondchancegarage.com/public/186.cfm

  10. #10
    Join Date
    Oct 2007
    Location
    Germantown, TN, USA
    Posts
    227

    Default Re: First vacuum test on manifold newbie with some tools

    I was at the boat this week and took a measurement for you on my 454 CIDs. After the engine is warm it will idle (out of gear) at 500 RPM with steady vacuum at 17 inches. Engine sounds great at this low idle. At 800 RPM it has vacuum of 19 inches. I run it at 800 RPM and when I engage the transmission the RPM dorp to about 700 RPM. Anything below 700 RPM and my transmission rattles so I don't go there. I use a 6 inch vacuum gage and the needle is steady to within .2 inch.

    Hope this is helpful.

    Chuck Hanson

  11. #11
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default Re: First vacuum test on manifold newbie with some tools

    are you tapping into your manifold directly or are you on the carb? how many hours on you top half? with 1200 hours I dont think i can expect what you just measured.

  12. #12
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,531

    Default Re: First vacuum test on manifold newbie with some tools

    Another Q for chuck; is your gauge damped?

  13. #13
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default Re: First vacuum test on manifold newbie with some tools

    Want to revisit the manifold presure before I haul out. I am trying to find out if the acutron vacuum gauge for $26 at autozone is damped and they cannot tell from the package. How importain is quality for this? Autozone fellow said he sells bunch of these and no complaints.

  14. #14
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,531

    Default Re: First vacuum test on manifold newbie with some tools

    call them and ask 1-800-ACTRON-7 (1-800-228-7667) & have the model number handy.

    My guess is that it is NOT damped

  15. #15
    Join Date
    May 2008
    Location
    Glen Head, NY, USA
    Posts
    362

    Default Re: First vacuum test on manifold newbie with some tools

    Looks like the OTC tools are much better quaility. specs dont list damped though. will call otc monday. anyone have comments about otc line of tools?

    http://www2.otctools.com/otctools.co...ucts/06-01.pdf

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