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needle and seat won't seal, gas tank too high?

Discussion in 'The Hokey Ass Message Board' started by myktrans, Nov 6, 2012.

  1. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member

    ok, so carb problems have been making me pull out my hair.

    i'm running a holley carb on a sbc. no matter what i'm getting fuel pushing past the needle and seat. float is good. needle and seat are brand new.

    the only thing i can think of is, the gas tank is mounted on top of the kick up and the motor is mounted pretty low in the chassis. but my old car was setup the same way and i never had any problems.

    it's so bad that it hydraulic'd the motor earlier while it was turned off and sitting. any thoughts would be appreciated......
     
  2. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    This isn't the answer to solving the problem but its not a bad idea in any case... I install shut off valves on my cars. Usually one at the tank and another just before the fuel pump.

    I doubt that the tank location is the problem but I'm certainly not an expert.....
     
  3. floats are not adjusted right.
     
  4. Ram Air Bob
    Joined: Oct 20, 2012
    Posts: 24

    Ram Air Bob
    Member

    MR Gasket used to sell clear plastic screws that seplace the brass screw that the float is set to. They can be a big help when a flooding problem is not responding, or the flooding is intermitant. You can just screw them in place, and set the float level with the engine running, with no fuel leaks.
     

  5. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    VoodooTwin
    Member
    from Noo Yawk

    Unless your tank is mounted 100 feet higher than your carb, that isn't the problem. What's your fuel pressure at the carb inlet? Are you running a racing type electric pump? Or a stock mechanical pump? How is it all plumbed up? The more info you can get us, the better.....
     
  6. Nonstop
    Joined: Jun 18, 2012
    Posts: 175

    Nonstop
    Member
    from CA

    Has the carb been rebuilt or adjusted? I assumed you checked the fuel pressure, but have you? Needle and seat are new, did you replace the old one because of this problem? Also agree about checkin float level.
     
  7. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member

    float level is set. stock mechanical pump. doesn't seem to be any trash in any of the filters and the whole fuel system is all new stuff. brand new. except carb but might as well be at this point.
     
  8. ac0j
    Joined: Apr 15, 2012
    Posts: 36

    ac0j
    Member

    Carb problem.
     
  9. All bikes have the gas tank above the carb so that is definately not the problem. Hold the bowl upside down and blow on the inlet. Raise and lower the float to see if it lets air through. I'm guessing way high fuel pressure!!
     
  10. Just noticed it hydraulic'd the motor? How about the no gasket on the seat or the seat being loose?
     
  11. I think you get about 1/2 pound of pressure for a foot of water. If your tank is 50 feet above the carburetor you would have 25 pounds of pressure. I do not know a thing about Holley carburetors. I am having trouble with a SBC loading up with fuel and I was told the floats are plastic and they go bad. I am not sure what the carburetor is on SBC but hope to check it out tomorrow when I find my small step ladder.

    Throw the floats in some water and see if they float. The needle and seat will not work with bad floats.
     
  12. carbking
    Joined: Dec 20, 2008
    Posts: 2,937

    carbking
    Member

    Two possibilities:

    (1) as mentioned by others, too much fuel pressure
    (2) as mentioned by others, carb float/fuel valve issue

    Too much fuel pressure can be caused by:
    (A) defective fuel pump
    (B) defective tank vent

    Carb float/fuel valve problem can be caused by:

    (A) defective float
    (B) defective fuel valve
    (C) cracked casting (rare)
    (D) adjustment

    Suggested procedure:

    (1) put a pressure gauge inline at the carb inlet and check the pressure
    (2) proceed with checking based on what the gauge tells you

    Until one experiences the problem, most would not consider the tank vent. A fuel tank MUST be vented. Once, back in the 1970's, we were experiencing fuel syphoning by vandals in the neighborhood. I placed a locking cap on my spouse's vehicle, not realizing the original tank cap was vented. As the car was parked in the driveway, when the sun warmed the day and also the tank, fuel expansion pushed fuel through the fuel pump, past the needle and seat, out the bowl vent of the carburetor, and DOWN ON THE DRIVEWAY!!! Put the stock cap back on the tank and solved the problem.

    Jon.
     
  13. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member













    thank you sir!!!!!!!!!!!!!!!! HA HA!!! i did notice it would seat and after i would drive around for a while it would just pour. sure as shit the gas tank was pressurizing! i'm gonna put a new vented cap on it. as soon as i read the first few lines of your post it clicked. thanks again!
     
  14. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,304

    henryj1951
    Member
    from USA

    i have seen back in the old days where they drilled a small hole ..even in the locking gas cap

    :cool:
     
  15. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member

    i just read the rest of your post. lol! i drilled a real small hole in the cap to test this theory. i'm 99.9% sure it's fixed now. crazy how you will overlook something so simple. :p
     
  16. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member


    was typing my last post as you posted yours. lol!
     
  17. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member

    just out of curiosity. how many pounds of pressure is a holley needle and seat good for?
     
  18. Have you checked for trash in the needle valve or seat? It doesn't take much more than a fly speck for fuel to get past it.


    I run mine @ 7psi but 6-6.5 is suggested.
     
  19. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member


    LOL! so true!
     
  20. myktrans
    Joined: Jun 27, 2012
    Posts: 79

    myktrans
    Member

    thank you everyone for your input!!!!!
     

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