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can fuel siphen out of carb?

Discussion in 'Chevy Trucks' started by loyboy, Apr 4, 2007.

  1. loyboy

    loyboy Member
    from KCMO
    Messages: 86

    83' chevy 1/2 ton w/ a sb400. If it sits longer than eight hours it won't start back up. No fuel in the carb. Pour gas in and it fires right up. Is this a carb. (quadrajet) problem or a mechanical fuel pump diaphram that's went bad? Thanks for any input.
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    More than likely it the "welch plugs" in the bottom of the main body of the carb that's causing your problem. When these leak, they allow the fuel thats in the fuel bowl to drain into the intake. Not at all uncommon on the Q-Jet carbs when they get old. If you don't know what a welch plug is, they're small lead plugs, kinda like a small frost plug that are pressed into certain passageways to block off holes in the carb after it has been drilled and machined. If you remove the carb and look at the underside of the main body you should be able to see 2 or 3 out of the 5 that are there.To get to all of them you have to remove the throttle base plate from the main body. To prevent this problem, when I do a rebuild on these, I always rough up the plugs and a small area around them and coat them with epoxy. That seals them up for good.
     
  3. loyboy

    loyboy Member
    from KCMO
    Messages: 86

    I think I'll try replacing the fuel pump as I have another one sitting around and they're easy to do. If that doesn't work, I'll pull off the carb. Thanks B&B. You always have neat and interesting info. It's much appreciated.
     
  4. hoss1

    hoss1 Junior Member
    from ohio
    Messages: 1

    check the fuel filter there is a one way valve in them to keep that from happening. If it is still in the carb.
     
  5. streetsurfin'

    streetsurfin' Senior Member
    Messages: 770

    Don't bother with the fuel pump. It runs once you prime and start it, correct? It is the welch plugs as stated. That gas is draining into your oil BTW so you lube is being diluted till you make the repair. HP Books - Rochester Carburetors, by Doug Roe, should be available at you local library and will give you the rundown on sealing them. If you can't find a book we'll help you get through it.
     
    Last edited: Apr 6, 2007
  6. streetsurfin'

    streetsurfin' Senior Member
    Messages: 770

    The fuel bowls are vented to atmosphere so a valve in the filter wouldn't prevent that would it? It may prevent the fuel line from draining back but the bowls empty and it still takes a while to fill them until the accelerator pump is primed.

    If you were to put on an electric fuel pump you could fill your bowl withought cranking the engine but you still have the issue of gas washing down your cylinder walls and draining in to your sump
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    lowboy, you can change out the pump but I don't think it's gonna solve your problem as even if the pump wasn't bolted on the engine, it should still start and run for a few seconds as there should always be some gas in the fuel bowl. If their isn't, then it's because it's leaking out through the welch plugs like I mentioned.
     
  8. wirenut

    wirenut Senior Member
    from nh
    Messages: 513

    my monte did that till i took the rubber o ring off the filler cap..
    when it does it go loosen the cap and listen,if you here a noise
    its vacume because the tank isnt being vented... at least thats
    seemed to be my problem..
     
  9. loyboy

    loyboy Member
    from KCMO
    Messages: 86

    Thanks for the input guys, I'll pull the carb this week and check out the welch plugs.:)