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WTF! My carb overflows with gas

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sample, Jan 29, 2003.

  1. Sample

    Sample 1/2 ton status

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    Another hurdle in my non stop process of getting this K5 to run properly.

    Little back ground on it. It has an electric fuel pump somebody swapped in before I got it, mounted to frame rail. I just rebuilt the carb about 2 weeks ago. It hasn't ran more than about 5 times only for a few minutes at a time since the rebuild of the carb.

    Last night, I was messing around with the blazer. I had the key in the accessory position for about 10 minutes. I started it, it ran really rough and blew tons of blck smoke. I was like WTF, so I popped the hood and took off the air cleaner, puddles of gas on the intake. I turned the key to acc. again to turn the fuel pump on. I watch as gas just fills the carb and begins to leak out of any orifice it can, especially around the accelerator pump shaft.

    What is the deal?
     
  2. Sandman

    Sandman 3/4 ton status Author

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    What kind of carb is it? You might have a bad needle and seat which could cause that.
     
  3. Sample

    Sample 1/2 ton status

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    Whoops, it's just the stock 4 bbl. Rochester Q-jet.
     
  4. Sandman

    Sandman 3/4 ton status Author

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    Might be a bad needle and seat then or you have something stuck in there thats holding it open. Its a common problem. Used to happen to me now and then.
     
  5. Sandman

    Sandman 3/4 ton status Author

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    Might be a bad needle and seat then or you have something stuck in there thats holding it open. Its a common problem. Used to happen to me now and then. Or the float might have become saturated and not foating anymore.
     
  6. pismorat

    pismorat 1/2 ton status

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    The fuel pump sounds like it is wired incorrectly too. It should not be pumping gas in the 'accessory' position, only in the 'on' position. Make sure the hot wire for the pump is connected to the ignition wire. I agree with the other guys about the carb, but you have to re-wire that pump. I have an auxillary elec. fuel pump that I wired through a switch so I can choose when to use it. /forums/images/graemlins/truck.gif
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Either the seat in the carb is bad or the pump has too much pressure. Might want to put a pressure gage on it. 4psi is plenty for a SB350. If it's 7-8 psi either swap it back to mechanical or put a pressure regulator on it.
    As for the wiring...I would put a oil pressure cut off switch in it (see jegs or summit). Wire it to the On selection. Wiring it that way would only alow the pump to come on once there is oil pressure. It's a safety feature.
    The carb should store enough fuel to start and idle before the pump kicks in when the oil pressure come up
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Hmmmmmmmm.......my electric pump is wired to come on in the aux. position. It's been working that way for over 8 years and I've never had a problem.

    If your float is working correctly, it should keep the needle down and not allow any more gas into the bowl AS LONG AS THE PUMP DOESN'T HAVE TOO MUCH OUTPUT PRESSURE. FWIW, my pump puts out about 4.5 PSI.

    In fact, I like the fact that the pump comes on before I turn the starter- that way the bowls are always full at start up.

    I'm willing to bet that your needle is stuck in the open position, brother. Sounds like it's time for a rebuild.....
     

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