Fuel leaking up out of filler cap in gpx250

Discussion in 'Australian Motorcycles' started by PeterCupit, Apr 19, 2006.

  1. PeterCupit

    PeterCupit Guest

    On my Gpx 250 fuel comes up and out the filler cap when the bike gets
    hot. I had the tank off and the overflow pipe is not blocked. The
    leak happens even when the tank is not full. I know that the seal is
    probably not too good (since turning the tank upside down causes the
    leak also (should this happen??), I don't understand how the fuel gets
    up to the top of the tank however (when it is not full and right side
    up on the bike).

    I don't know if it's related but I had a few days ago a sump full of
    oil and petrol ... Changed the oil last night and it seems ok now.
    The fuel petcock seems to be turning of (there is a bit of a dribble
    after it does turn of) - checked by sucking on a straw on the vacuum

    A little confused what to check - probably need a new gasket on the
    fuel cap but I don't think this is the complete problem since fuel
    leaks out the key hole...?

    Any ideas would be appreciated.


    Peter Cupit
    PeterCupit, Apr 19, 2006
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  2. PeterCupit

    Rod Bacon Guest

    Are you sure you're not running the bike with the fuel tap in the PRIME
    Rod Bacon, Apr 20, 2006
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  3. PeterCupit

    PeterCupit Guest

    There is no prime position on this bike, I had to put a vacuum on the
    petcock ( with a straw ) to get the thing to start - there is only
    reserve, on and off. Fuel flow is meant to only occur when engine
    PeterCupit, Apr 20, 2006
  4. PeterCupit

    Rod Bacon Guest

    What year is the GPX?
    Rod Bacon, Apr 20, 2006
  5. PeterCupit

    PeterCupit Guest

    PeterCupit, Apr 20, 2006
  6. PeterCupit

    BT Humble Guest

    How did you check this? Can you blow through it while it's connected
    to the tank?
    It certainly sounds odd.
    The vacuum petcocks do tend to fail eventually, on mine it was at the
    15-year-old mark. It failed in that the vacuum function no longer did
    anything, so the tap became a "standard" one. If yours didn't turn off
    properly (ie. the dribble) and one or both of your carburettor float
    valves is a bit dodgy then that's probably how you got a sump full of
    Well, it sounds like your fuel tank is somehow getting pressurised.
    The leakage might be fuel vapour condensing on the upper (inside)
    surfaces of the tank and getting forced out by the pressure, but that's
    just a wild-arsed guess on my part.

    BT Humble, Apr 20, 2006
  7. PeterCupit

    PeterCupit Guest

    I checked the overflow connector with a car tyre pump - air got through
    ok... (Now that I think of it anything else in the pipe would have got
    through also..) The pipe itself I checked the same way - it does need
    to be replaced as it has a rip in it.

    I don't think the overflow is working even through it isn't blocked.

    I talked to a guy at a bike shop here in Nowra and he is suggesting
    that the internals of the fuel cap are faulty - had no idea it had
    anything complex in it..

    Peter Cupit
    PeterCupit, Apr 20, 2006
  8. PeterCupit

    Knobdoodle Guest

    [confused face]
    There's two types of bike taps.
    "Normal" on-reserve-off or
    "Vacuum" on-reserve-prime (and no fuel flows when the engine isn't running
    unless it's in "prime").
    Knobdoodle, Apr 20, 2006
  9. PeterCupit

    BT Humble Guest

    They've got a few parts to them, as you'll find out if you start
    disassembling one. ;-)

    Have you got the service manual I made up? Do a Google for
    "GPX250Manual.pdf" and you should turn up a copy.

    BT Humble, Apr 20, 2006
  10. PeterCupit

    G-S Guest

    I nearly suggested a stuck fuel cap, but I thought... nah with all the
    complicated stuff you are talking about you'd already have checked that :)

    Do you get a pressure 'woosh' often when you open your tank?

    G-S, Apr 20, 2006
  11. PeterCupit

    john doe Guest

    (if he can't work out that for himself bikes may not be a good idea)
    john doe, Apr 20, 2006
  12. PeterCupit

    Rod Bacon Guest

    Datz zacchery wot I woz finkin'.
    Rod Bacon, Apr 20, 2006
  13. PeterCupit

    BT Humble Guest

    You'd think that would be the sensible thing, wouldn't you?
    Unfortunately Kawasaki decided that for the GPX250 what you really want
    in a vacuum fuel tap is Off-Reserve-On.

    Even when you set it to "reserve" you still need to have engine vacuum
    before fuel will flow, so if you've cleaned the carbies you need to
    either use a bit of suction hose to prime the carbies or hope that your
    battery will crank the bike over for long enough to fill them.

    BT Humble, Apr 20, 2006
  14. PeterCupit

    PeterCupit Guest

    I think my tank vent isn't working...
    PeterCupit, Apr 21, 2006
  15. PeterCupit

    PeterCupit Guest

    btw thanks to all who posted
    PeterCupit, Apr 21, 2006
  16. PeterCupit

    Peter Guest

    or roll start :-( very undignified.
    Peter, Apr 21, 2006
  17. PeterCupit

    Knobdoodle Guest

    Well bugger me!

    My apologies Peter.
    Knobdoodle, Apr 21, 2006
  18. PeterCupit

    PeterCupit Guest

    There is sometimes a slight pressure release. Before last week I had
    not thought about the whole pressure release system should work. Now
    that I have taken the cap apart and seen the little gaskets, small
    holes and channels and etc in there it's pretty clear that the most
    likely failure isn't the overflow pipe getting blocked. Still
    hard to know which bit of the cap is faulty - suspect either the rubber
    seal on the key barrell or the big paper? gasket just under the cap
    (there are little channels just here where the fuel flows in and then
    out when the pressure is high enough) The little rubber pressure
    'sensors' seem ok so I think the pressure just gets high enough to
    breach the top gasket before the rubbers things let it out around to
    the overflow.

    btw none of the holes or channels in the cap were blocked...

    New assembly costs $119, might try to make a new paper gasket for the

    PeterCupit, Apr 22, 2006
  19. PeterCupit

    Theo Bekkers Guest

    So, are you in your prime? Then there's the tap on the Moto Guzzi Sabre.
    Vacuum tap, no prime.

    Theo Bekkers, Apr 23, 2006
  20. PeterCupit

    Theo Bekkers Guest

    "Knobdoodle" wrote
    There's more than two types of bike taps Clem. Mine has on and off, no
    reserve. The Sabre Helen had had two screw type taps which could only
    be accessed by removing the sidecovers (they were only there so you
    could remove the tank) and a vacuum operated flow gadget in a place
    impossible to access. The scooter has no tap and a vacuum flow control
    valve also.

    Theo Bekkers, Apr 28, 2006
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