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Hot Rods Vacuum leak

Discussion in 'The Hokey Ass Message Board' started by Fourdy, Mar 29, 2020.

  1. Fourdy
    Joined: Dec 9, 2001
    Posts: 454


    I have a Holley 570 new carb on an air gap manifold that I can not get to idle below 1000. Runs a short time then dies. Checked and found that when I sprayed starting fluid around the carb when I got to the front of the carb the engine smoothed out and raised rpm. Okay, took the carb off and replaced the 2 gaskets with 2 new ones. (Holley) These had the metal plate that is used to mount the throttle and TV cable. Same problem. The base of the carb and manifold both look flat. The carb base does however have the circular milling marks but very faint. Since I can't get in touch with Holley for a couple of days I have a QUESTION?

    Is there any kind of non-hardening, fuel proof gookum pucksy that I can use on the gasket surfaces to see if I can stop the leak?

    Thank you for any assistance,

  2. 5brown1
    Joined: Apr 13, 2008
    Posts: 206


    try Seal All. It is a contact adhesive and sealant. I have used it to seal a leaking gas tank.
    About any hardware store will have it. I don't believe it is non-hardening though. I would think it can
    be removed from hard surfaces fairly easily.
    Joined: Mar 21, 2014
    Posts: 711

    from okc

    Yamabond, Honda has a similar product also.....
    Desoto291Hemi likes this.
  4. BJR
    Joined: Mar 11, 2005
    Posts: 7,052


    Are you sure you have the correct gasket for the manifold? A friend had a problem like that on a Pontiac 3x2 setup. Turned out the gasket had a vacuum channel in it and the manifolds shape under the gasket dipped in just enough to catch the channel causing a vacuum leak. He got solid gaskets with no channel and problem solved. I doubt the milling marks are causing the leak. Also see if the gasket covers the bottom of the carb correctly. Hope the way I explained this made sense.

  5. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,374

    Tickety Boo
    from Wisconsin

    How about some pictures :rolleyes:
    Desoto291Hemi and Deuces like this.
  6. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 2,638


    Explained perfectly @BJR. I had the same problem with a Quadra-junk on an old Torquer manifold. Took me forever to figure out it was the gasket...and not the carb. Finally got a gasket that matched the intake (solid) instead of the one that matched the carb.
    Deuces likes this.
  7. saltflats
    Joined: Aug 14, 2007
    Posts: 10,901

    from Missouri

    Are all the unused vacuum ports capped off?
    Deuces likes this.
  8. Positive the manifold or the carb is not warped ?
    Deuces and Sporty45 like this.
  9. Sporty45
    Joined: Jun 1, 2015
    Posts: 998

    from NH Boonies

    Yup, definitely need to check this first.
    VANDENPLAS and Deuces like this.
  10. Fourdy
    Joined: Dec 9, 2001
    Posts: 454


    The only place that indicates a leak with starter fluid is at the front of the carb at the manifold/carb line. Today I will take the carb off and remove the holley metal plate between the gaskets as well as check for warping. Try running without the plate and just one gasket??

    Working with a new Blueprint Engines 405 hp, vortec roller cam with air gap intake in my 40 Tudor Ford.

    Again thank you and I will keep trying.

    Deuces likes this.
  11. Tri-power37
    Joined: Feb 10, 2019
    Posts: 510


    At work we have a “smoke machine “ made by Snap On that is great at diagnosing vacuum leaks. If you could beg or borrow one somehow they are very easy to use.

    They feed a inert smoke into the intake system and vacuum leaks show themselves pretty readily.
    egads likes this.
  12. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,431

    from illinois

    A decent straight edge and a bright backlight then feeler gauges will usually help find wasrped surfaces quickly , anything over .005 can present a problem , under .005 the gaskets should do their job.
    Deuces likes this.
  13. Before you take the carb off, look at the offending area with a mirror and flashlight. You may see what the problem is. So if you have a plate in there the stack from the bottom up should be:

    Make sure the plate is flat, mark up the intake and carb base with layout dye or a Sharpie, run a flat file across the surfaces. Put something in the intake to catch any filings.. don't forget to remove it. Make sure all hardware on the carb itself is secure.
  14. 40FORDPU
    Joined: Mar 15, 2009
    Posts: 3,122

    from Yelm, Wa
    1. Northwest HAMBers

    Identify vacuum leak-correct it-leave sealer in cabinet.
  15. Fourdy
    Joined: Dec 9, 2001
    Posts: 454


    Took the plate off and installed again with one gasket after re-torquing the intake. Check manifold and carb for flatness with nothing apparent with a bright light. Very light rev rise spraying the throttle shaft. (hardly detectable) Okay, take the carb off and put the 80570 Holley from my blown flatty and try it. Viola! Ran and idled beautifully. I could shift the 200-4r thru the gears and have the fan come on without killing the engine even.

    Spent two 30 minute waiting sessions to speak to Holley tech but now answer. (must be closed for C9)

    New ?? Where do I start with a Holley that won't idle? Oh, float levels are right on. Runs great from 1000+ rpm on.
    Thanks for hanging in with me.

    warbird1 likes this.
  16. silent rick
    Joined: Nov 7, 2002
    Posts: 4,376

    silent rick

    what's a small fiddle got to do with it?
    David Gersic, 427 sleeper and egads like this.

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