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  1. #1
    Duke's Avatar
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    Gas tank pressure

    For carbed GPRs

    Why do we have it?

    How is it regulated?

    Is it just a oneway valve on the vent that causes it?

    When do you know if its to much?

    Will it just continue to rise until it pops the needles off their seats?


  2. #2
    All hail the Chief! fullboogie's Avatar
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    Duke,

    It's to assist the weak little pumps in the carbs. There's a one way valve in the vent line that keeps the pressure regulated. Never heard of it malfunctioning and causing too much pressure...

  3. #3
    2000 GPRXP 4tec shooter98xpl's Avatar
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    There is a vent tube going out the side of your ski, under the fairings. Trust me when I say this, if that tube is not set right, it will implode the tank. I did this with my efi gas tank. It took me a while to figure out what the hell caused my tank to implode, but after blowing through some hoses I figured out what I did wrong.
    Even in the EFI skis, the pressure builds up in the gas tanks, just like it does in your vehicle.
    Never seen one pop a needle and seat and leak fuel, I think that the vent valve opens up before it gets to a certain pressure. Its a check valve.
    Hope this helps.
    SHOOTER

  4. #4
    Tool Bag water worx's Avatar
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    On the hottest day it only builds like 1 to 2 pounds of pressure,it takes a lot more to pop the needle,but if the needle gets stuck with a piece of debris....look out,you got a motor full of fuel.

  5. #5
    Duke's Avatar
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    I'm confused. How does a oneway valve regulate pressure?

    My 1200 always has pressure in the tank. The "FUEL" pressure is always out of wack and fluctuates highly on this boat.

    The ported ski never has pressure in the tank and "FUEL" pressure is rock solid.

    Both have new fuel pumps and the same gauge was used on both boats.

    When I refill the 1200 on the water for the second half of the trip it acts like its running out of gas for a little while.

  6. #6
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Hello Duke, What that valve is for is if you flip your ski over you do not have fuel leaking in the water. On my xll i have taken the valve out because my valve was sticking. The oil tank has one to.

  7. #7
    Moderator beerdart's Avatar
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    Quote Originally Posted by Duke View Post
    I'm confused. How does a oneway valve regulate pressure?
    A one way valve (Check Valve) Has a spring holding it shut the spring rate is known as cracking psi. It is like a Jet Works Valve with a set spring rate. Typical cracking psi for fuel tank vents is aprox 2-3 psi. You can also think of it as a in line relief valve. The fuel system will have two valves one for sucking and one for relieving.

  8. #8
    Duke's Avatar
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    Quote Originally Posted by beerdart View Post
    A one way valve (Check Valve) Has a spring holding it shut the spring rate is known as cracking psi. It is like a Jet Works Valve with a set spring rate. Typical cracking psi for fuel tank vents is aprox 2-3 psi. You can also think of it as a in line relief valve. The fuel system will have two valves one for sucking and one for relieving.
    I understand how the valve works just not how on this system. The valve lets air in but not out, no sring just a cheap plastic ball. It doesn't matter how much air pressure I put on it nothing comes out of the tank side.

  9. #9
    Duke's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    Hello Duke, What that valve is for is if you flip your ski over you do not have fuel leaking in the water. On my xll i have taken the valve out because my valve was sticking. The oil tank has one to.
    I'm thinking your right Jim, not that I ever didn't. So its not really a vented system. Just lets air in as the fuel is depleted so as not to create a vacuum against the fuel pumps.

  10. #10
    cheatin' piston popper addicted's Avatar
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    I think worst case, if you are running low popoff, it could open the needles up if it's baking in the sun all day. Pressure is usually relieved when the carbs suck the gas from the tank., and the check valve lets fresh air in when the tank is almost under vacuum. The pressure in the tank also assists the fuel pumps. I am not aware of any kind of pressure relief valve.

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