Carb vacuum leak!

Discussion in 'Holley' started by buick64203, Oct 10, 2021.

  1. buick64203

    buick64203 Just plum crazy Staff Member

    So I'm working on this 79 New Yorker. 360 magnum with a factory Holley 2 barrel. The car had a significant vacuum leak and hardly ran. The carb was junk.

    The customer got me a carb off rock. Put it on Friday and ran pretty good. Put my vacuum gauge on it and it was pulling about 17 inches. Not bad....figured it was fixed.

    Start it up yesterday and it's back to a massive vacuum leak. I cannot find any external leak. Plugged up and pinched off every vacuum hose. Sprayed carb cleaner everywhere. It's gotta be internal to the carb

    The old carb was so bad the engine hardly ran. With this carb, at least the engine runs.

    Would debris in the fuel clog something up internally? I put a new fuel filter in and purged the line. I just can't seem to figure this out. I wish j could put this carb on another engine to rule it out.

    Any suggestions? advice? Im at a loss here
  2. Smartin

    Smartin Staff Member

    Clogged idle circuits will cause symptom similar to vac leak. Pull apart carb and make sure every little orifice is clear. Blow out with compressed air and reassemble
  3. mrolds69

    mrolds69 "The Cure"

    Did you compare them really carefully before r+r-ing? Rebuilt carbs often have the wrong base plate, air horns or whatever. You checked the base gaskets carefully?
  4. 12lives

    12lives You die once. You live every day.

    you can pull a strand of copper electrical wire to clean the small orifices.
  5. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    You can Also use the old timers trick Jason . Suck on the carb . Start it up and rev it up to about 2500 or so and choke off the venturi With your hand and when it almost stalls out remove your hand and feather the throttle . Do this about 3 times and see what you turn up with . Its worked numerous times for me .
    Dano likes this.
  6. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Pull the oil fill cap and place your hand over it. The intake gasket could be leaking. I can't answer why it would be temporarily fixed though.
  7. buick64203

    buick64203 Just plum crazy Staff Member

    In answer to Frank's question- yep, they are identical. Same number and everything.

    Im gonna try the "suck it through" trick today if it ever stops raining. And if thst doesn't work, I'll reluctantly take the carb apart and blow it out
    mrolds69 likes this.
  8. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    Have you done it before Jason ???
    Dano likes this.
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If the carburetor came from Rockauto, it's probably re-manufactured. You know how re-builders like cliff Ruggles feel about re-manufactured carburetors. Take the original over to Allstate.
    Smartin likes this.
  10. TORQUED455

    TORQUED455 Well-Known Member

    What are the symptoms that cause you to say “massive vacuum leak”? Is it just an idle problem? Have you tried propane enrichment or closing the choke blade a bit to richen it up? Does this engine use an EGR valve?
  11. buick64203

    buick64203 Just plum crazy Staff Member

    I should say it's lean as F. If I choke it out, the idle goes way up and the AFR goes down to a reasonable 13 to 1.

    It does have an egr. But it doesn't seem to be leaking
  12. TORQUED455

    TORQUED455 Well-Known Member

    Have you tried adjusting the idle mixture? Does it run OK at cruise or WOT? Can you check to see whether the EGR valve is sticking open? If you road tested the car with the new carb, maybe the EGR valve opened and is stuck open now??
  13. buick64203

    buick64203 Just plum crazy Staff Member

    See? That's why there are two police officers in a car....because one guy cant think of everything!
    FLGS400 likes this.
  14. Dano

    Dano Platinum Level Contributor

    I have Lou & have had it work.
    gsx455-4ever likes this.
  15. buick64203

    buick64203 Just plum crazy Staff Member

    Im going to take a closer look at the egr valve today and report back.
    Max Damage likes this.
  16. Max Damage

    Max Damage I'm Working on it!

    Seems crazy that two carbs in a row would have such similar issue? Maybe there is some kind of small crack or hard to see leak in the intake?

    Just for people who may not be aware (not Jason)
    Rebuilt carbs often are not properly setup for particular applications. They may require adjustment/bending of linkages and tuning. Or rebuilding LOL.
  17. telriv

    telriv Founders Club Member

    I seem to rememer EGR valves didn't come into play until around '73 or so by the OEM's. I could be wrong BUT maybe that's NOT a '70 manifold???

    Tom T.
  18. Smartin

    Smartin Staff Member

    It's on a 79 New Yorker
    TORQUED455 likes this.
  19. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    Use propane to check for a leak.
  20. Dano

    Dano Platinum Level Contributor

    If it ran decently with the new carb & then started to running like crap again, sure seems like the carb is the problem.

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