odd fuel leak, holley 600 vs
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odd fuel leak, holley 600 vs

  1. #1
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    Default odd fuel leak, holley 600 vs

    Fuel is dripping off the bottom of the rod coming out of the vacuum diaphragm for the secondaries. I took the bowl off and needle seems to be okay, and I blew it out.

    Any idea where the leak could be coming from?

    This is only on the rear carb on my tunnel ram.

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    gn7
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    There is no fuel connection between the under side of the secondary diaphragm and any fuel in the carb. The under side of the diaphragm is open to the atmosphere.

    If you have fuel there, it is either coming thru the top side of the diaphragm which it still shouldn't have fuel because thats suppose to be in a vacuum as the engine speed increases.
    I'd check to see if the fuel is being sprayed onto the diaphragm housing while your driving.
    If its happening on the trailer, or while the boat isn't moving, then you must have some serious fuel running into the venturi and then to the top side of the diaphragm. And even then, it should never be on the lower side of the diaphragm.



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    Gonna sound crazy, but I assume this is happening and being noticed after being underway. Sideways mounted carbs I would assume, but can it be that the front carb is spraying fuel that the rear carb is "catching" and absorbing through a leak in your vac diaphragm housing?

    Sounds like a very weird one to me.......

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    AKA Blownjet 468 Blowncat 509's Avatar
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    are you sure it's not coming out of the secondary throttle shaft area? those get
    pretty loose sometimes, ....


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    thanks for all the responses guys.

    This is happening at idle after brief run times n the trailer....I really can't tell where its actually coming from...

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    how sloppy is the secondary throttle shaft? if you can wiggle it, you can throw in the
    teflon wrap bushings that come in most Holley kits- (they are the little white coiled up
    things that most people throw away,cuz they don't know what they are) they usually
    work pretty well


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    Quote Originally Posted by Blowncat 509 View Post
    are you sure it's not coming out of the secondary throttle shaft area? those get
    pretty loose sometimes, ....
    Unless the shafts use some sort of positive seal it will not make any difference if they are loose or tight...the presence of fuel on the throttle shafts indicate dripping from the booster venturis or leakage from the idle/transfer circuit. Wear on the throttle shafts means nothing in regards to fuel dripping from the shafts.
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    gn7
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    None of this makes any sense. At an idle the fuel is discharge below the throttle shafts anyways. Its not coming from inside the carb. It has to be an exteernal leak from a bowl gasket or accelerater pump housing or something like that.

    You could shut the butterflies, and fill the carb to the top with fuel and not have it drip from the secondary diaphragm rod.



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    058
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    Quote Originally Posted by gn7 View Post
    None of this makes any sense. At an idle the fuel is discharge below the throttle shafts anyways. Its not coming from inside the carb. It has to be an exteernal leak from a bowl gasket or accelerater pump housing or something like that.

    You could shut the butterflies, and fill the carb to the top with fuel and not have it drip from the secondary diaphragm rod.
    Look closely at the vac. diaphram connecting link at closed throttle. The connecting point is slightly below the throttle shaft. Fuel can run out of the bore[s], out the throttle shaft down to the lowest point, the connecting pin. Fuel can be pushed out of the transfer slot due to cross channeling or percolation and onto the throttle blades to the shaft. When dealing with internal leakage problems the 1st place I look for fuel leakage/dripping is the needle/seat assem. O ring. They usually flatten with age and allow fuel past the O ring causing uncontrolled float level. As for the accelerator pump housing, it's on the other side of the carb opposite the vacume diaghpram...but you knew that.
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    gn7
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    Quote Originally Posted by 058 View Post
    Look closely at the vac. diaphram connecting link at closed throttle. The connecting point is slightly below the throttle shaft. Fuel can run out of the bore[s], out the throttle shaft down to the lowest point, the connecting pin. Fuel can be pushed out of the transfer slot due to cross channeling or percolation and onto the throttle blades to the shaft. When dealing with internal leakage problems the 1st place I look for fuel leakage/dripping is the needle/seat assem. O ring. They usually flatten with age and allow fuel past the O ring causing uncontrolled float level. As for the accelerator pump housing, it's on the other side of the carb opposite the vacume diaghpram...but you knew that.
    Yeah I knew the accel pump housing was on the other side, just thinking it could cling to the bottom of the bowl as it traveled across the bowl. Seen crazier things
    As for the linkage, you have me there. Thats what I get for not playing with a vac secondary carb for over 30 years Thanks for the input, Good to know.



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    Hi guys, thanks for all the suggestions.

    I ran it one day and it seemed that it was fine, but then the next day it came right back.

    I'm fairly certain its some sort of bowl flooding issue, as I can take off the fuel level plug and fuel just pours out.

    Now, like i said, needle and seat seem to be fine.

    Front (primary) float, and fuel level is dead on. But I do have that (I forget the exact name) equalizer tube that runs from the front bowl to the rear bowl...could the rear flooding be caused from the front filling the rear?

    Thanks.

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    gn7
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    Quote Originally Posted by PowerAddict View Post
    Hi guys, thanks for all the suggestions.

    I ran it one day and it seemed that it was fine, but then the next day it came right back.

    I'm fairly certain its some sort of bowl flooding issue, as I can take off the fuel level plug and fuel just pours out.

    Now, like i said, needle and seat seem to be fine.

    Front (primary) float, and fuel level is dead on. But I do have that (I forget the exact name) equalizer tube that runs from the front bowl to the rear bowl...could the rear flooding be caused from the front filling the rear?

    Thanks.
    The "transfer tube" act as nothing more than a fuel line for the secondaries. The floats still act independent, and one has no effect on the other. Fuel is present in the transfer tube under pressure anytime the engine is running.
    Not sure why you think the needle and seat are ok. Blowing in them is worthless. If you remove the float sight screw and fuel pours out, you need to look at the needle and seat again. Or more correctly, think about replacing it. The only way fuel can entire the bowl is past the needle and seat for ITS bowl.

    FYI, if the o-ring on the outside of the needle seat assembly is flattened, or cracked, or in anyway not perfect, you'll never be able to hold a fuel level with it.



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    Last edited by gn7; 06-01-2011 at 05:52 PM.

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