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fuel pressure 94 carb

Discussion in 'The Hokey Ass Message Board' started by guy1unico, Sep 14, 2008.

  1. guy1unico
    Joined: Aug 30, 2006
    Posts: 924

    guy1unico
    Member

    Do you know what to do if fuel runs over the carb bowl and the Holley 427-12804 low ressure regulator / the arrow bounces around between 1 -2 psi. Note I cleaned the carb and checked the float @1 3/8"

    Things were working ok until I took the screw completely out of the pressure regulator / then screwed it back to where it was ...now the arrow bounces around & my carb bowl overflows. Let me know / if you know where to start with the fix.

    This whole car is really clean motor included but it would fizzle out and flat dye occasionaly so I started messing with the fuel system ... probably never should have.

    Thanks for the help,
    Guy
     
  2. skwurl
    Joined: Aug 25, 2008
    Posts: 1,620

    skwurl
    Member

    I'm not sure axctly on your particular regulator. I have aHolley regulator on mine. Clockwise increases pressure and counterclockwise decreases. It is kinda backwards to me. I figured screwing it in would block off the port more alowing less fuel. I learned it the hard way I was ruuning about 6lbs on mine till I put a good guage on it and could actually see what I was doing. Also if youre running an electric pump it may not get the pressure down to th 1-2 psi range. Good luck.
     
    Last edited: Sep 14, 2008
  3. John O
    Joined: Aug 26, 2006
    Posts: 96

    John O
    Member
    from Central NJ

    I've been experiencing the same issue with my setup. 3 94s on a Y-Block. Same pressure regulator with a liquid filled guage. Start the car, set the pressure to 3lbs and as the car warms up the pressure drops. Adjust it back to 3 and everyones happy. Start the car the next day and the pressure is up around 5 and the carbs drip. ??? I've been told that the liquid filled guages are the cause of the percieved variation in pressure. As the liquid warms from engine heat it thins and the needle moves easier. Conceptually it sound good but I think it's BS. I have'nt fit a new pressure guage to test it yet.
     
  4. skwurl
    Joined: Aug 25, 2008
    Posts: 1,620

    skwurl
    Member

    I don't run a guage all the time. I just set it at 2.5 lbs and took the guage back off. 3lbs is a little too high for thse carbs. I havent had any issues since setting it. The fuel pressure should not increase due to the guage since it is after the regulator. I also have a mechanical pump. Electric pumps flow a lot more.
     

  5. Andamo
    Joined: Jan 10, 2006
    Posts: 501

    Andamo
    Member

    Think of the regulator as having a downstream port (inlet) and upstream port (outlet) with a spring between the two ports. The spring pressure is probably in the 0# to 10# range. When the adjustment screw is backed out the entire way, you basically have no regulation of the fuel. As you screw the adjustment in ( clockwise ) you're putting more pressure against the spring and more pressure to the upstream port that goes to the carb inlet. Inexpensive gauges have poor linkage connections between the bourdon tube and the needle that reads the pressure and this, along with engine vibration might be the cause of the bouncing needle. Or it could be seeing the pulsations of the pump be it electric or manual.
    And yes, the liquid filled gauges are affected by temperature since it's silicone it uses as the needle dampening fluid. Silicone when cool or cold is more viscous and becomes "thinner" when warmed. Mass produced inexpensive regulators are prone not to be able to hold the set pressure, especially in the lower range of the spring or if the spring has too wide of a range like 0# to 20# or higher. Some regulators are stamped with the range of the spring.
     
  6. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Gauges are another issue...not only is quality pretty random in aftermarket ones, I think all currently available stuff for automotive fuel pressure applications is 0--15, so with antique carbs of any sort you are working well away from what the gauge was designed for AND you are getting as gauge that is hard to read because the needle is practically lying on the floor.
    The answer probably would be to use some sort of industrial gauge made for a very low range of pressure for setup only, removing it and keeping it as a tool for actual use to avoid the safety issues. The lowest pressure gauge I have is a 10lb fuel one, and that's an antique. I'd like to see a good 5lb one...
     
  7. dickster27
    Joined: Feb 28, 2004
    Posts: 3,169

    dickster27
    Member
    from Texas

    There you go Bruce, show your real stuff buddy, manufacture one. I will be a great customer for a 4-5 lb. gauge.
     
  8. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    Where do you get a good regulator. Why didn't they come factory on the engines?
     
  9. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    I also had the issue with my liquid filled Moon fuel pressure gauge, and couldn't figure it out..The temperature is the issue..When it cold the needle has a hard time moving in the thick liquid and of course when it get warm it will give you and accurate reading..So, set it when it's warm and it will be good..I'm using a Holley LP fuel regulator 0 to 5lbs, with a carter electric fuel pump..
    Make a good pressure guage I would also use them.."GET IT DONE" Bruce..
    Duane.
     
  10. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    Thanks 97, ordered the holley lp fr. I have a moon guage that I don't use. It goes up to 150lbs. Kinda hard to see the needle different from 2-4lbs :]
     
  11. Andamo
    Joined: Jan 10, 2006
    Posts: 501

    Andamo
    Member

    That's the problem in using a too high of a gauge pressure range. For the best accuracy in setting the pressure, you need a gauge to be closer to the amount of pressure you need to achieve. Even a 0 -15# would be better. Make sure the pointer is setting on 0. If it's not on 0 it means the gauge was overpressured and the bourdon tube has been stretched or the gauge was dropped or handled roughy and the accuracy has been lost.
     
  12. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    "Where do you get a good regulator. Why didn't they come factory on the engines?" Pressure was regulated by the diaphrgm spring in the stock fuel pump. Now, you have to check even that, because fuel pump innards have a lot of interchange and a new pump is very likely to have a 5 or 7 pound spring from some more modern application...save your old dead pumps, you may need their springs!
     
  13. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    Bruce, your right again..I've had lot of people say my carbs are flooding and can't figure out why.." I'm running a stock fuel pump".. I tell them to put a gauge on it and see what actual pressure their getting..OOPs..5, 6, 7 lbs..to much..
    Duane.
     

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