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Fuel Draining Continuously 600ss

Discussion in 'Supersport (1974-2007)' started by DanSS600, Jul 16, 2020.

  1. I filled the tank and as I walked to pay realised there was petrol running out of the overflow pipe by the rear brake pedal. Thinking this was just a minor over filling I expected it to stop quickly but it didnt. The fuel was pouring out for about 5 minutes. No key in the ignition so the pump was off.

    I had a pencil in my top pocket so plugged the hose with it and rode home without a problem.

    The bike is new to me and this is only the second time I have filled it - there was no leak last time.

    Any ideas?
     
  2. maybe some dirt in the carbs stopping the float valve shutting off
     
  3. The hose the fuel is running out of is one of the three connected to stubs at the back of the tank by the hinge not the drains from the carbs. You can just see it in this pic running down between the frame and the back of the gearbox and ending under the oil sight glass. hose.jpg carbs.
     
  4. Does the 600 have a rubber vent tube on top of the tank with a small cylindrical aluminium one way valve in it?, if so the valve isn’t operating properly, it should allow air in but not petrol out, although I suspect you overfilled as well, if it has the valve as my description above let me know and I’ll post a link to a cheap alternative to £50 Ducati one.
     
  5. Yes, it has this valve
     
  6. Ok, take the valve off and blow through it, it should only allow air through in one direction, if it allows air in both directions it’s had it and needs replacing, it stops fuel coming out when you brake but allows air in so you don’t get a vacuum in the tank, I’ll post the link to the cheap valves in a minute, you need the 6mm version.
     
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  7. https://www.ebay.co.uk/itm/123873039474
     
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  8. Thanks Mark that is a great help. Should the arrow point away from tank or towards it?
     
  9. I always forget, that’s why I blow through em to find out, best guess is the arrow shows direction of flow so should point towards the back of the bike, but blow through it to be sure.
     
  10. Arrow points away from the tank, ie forward.
     
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  11. Cheers Carr, I replaced mine with one ref the link above, good little unit but no arrow so the blow job is essential when using those :)
     
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  12. I think the direction of the arrow depends upon the manufacturer of the valve.
    The Ducati valves have an arrow head, not what I would call a propper arrow. The arrow head in this case represents the valve seat & not the direction of air flow.
    The valve should be fitted so that it allows air to enter the tank, (to prevent a vacuum within the tank & so fuel starvation) but prevents/blocks fuel venting out of the tank.
     
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  13. It could be the hose inside the, tank when you open the filler cap you'll see a small hole it's meant to drain any excess spillage when you fill up, if that drops off the spigot it will half drain the tank. You might be able to feel what's going on and stick it back on or you'll have to take the whole cap assembly out to re attach it.
     
    #13 rhubarb and custard, Jul 16, 2020
    Last edited: Jul 16, 2020
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  14. It’s always difficult to diagnose remotely, my theory that it’s the valve is an easy one to check but I must admit I’m a little confused as to how the petrol would overflow with the bike stationary because with the bike on it’s sidestand the vent would be at the highest point of the tank, it certainly happens under braking if the valve is gone, that’s what happened with my 900ss until I changed the valve, it could be as Rhubarb describes above, but as always go for the simple to check items first, let us know the outcome please, nothing worse than a thread left hanging:)
     
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  15. Thanks, new valve ordered.

    The only good thing about the event was they didn't charge me for the £11 of fuel.

    I will try to get time to look at the problem today and update
     
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  16. I agree. The drain hose has either come off or split inside the tank.
     
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  17. When you stop to fill up you are filling up with cold fuel, (from an underground storage tank) & putting it into the fuel tank sat on top of a hot engine, who's temperature is increasing, (for a short period even though it is switched off). The ambient temperature also can have a big affect on this happening too.
    Obviously the fuel expands quite rapidly & because we tend to fill our tanks it doesn't take much to overflow. Usually at most this might mean a few drops coming out of the tank & might not even be noticed. However, if fuel starts syphoning out of the tank once this has started it will not stop by itself until the fuel level drops below where it is escaping from.
     
  18. yeah I don’t think the fuel expands Cat or at least not to a large degree but it certainly gives off a lot of fumes and the air inside the tank expands with the heat also.
     
    #18 Mark9, Jul 17, 2020
    Last edited: Jul 17, 2020
  19. Everything expands with heat, to varying degrees, but it does expand. That is why aircraft always fill up by weight of fuel rather than gallons or litres of fuel.
    A cold gallon of fuel takes up less space than a hot gallon of fuel.
     
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  20. not disputing that, I worded it badly and went back and updated it, you must’ve taken the quote before I had done so, what I meant was I thought it unlikely that it would expand to the degree that it would cause the overflow, it’s difficult for any of us to diagnose without having been there but good that we all give suggestions of course, it should be easy enough for the OP to get to the bottom of this once he does his checks/changes and refills.
    UPDATE: just found this;
    Gasoline does expand and contract a little depending on its temperature. When gasoline rises from 60 to 75 degrees F, for instance, it increases in volume by 1 percent while the energy content remains the same.

    UPDATE 2; I recon that’s a potential 160cc of expansion in 16 litres of fuel,(but my maths is crap please check that!) roughly half a household tea mug, so is it possible that if the OP absolutely brimmed the tank, and although the bike was leant on it’s sidestand the fuel was close enough to the vent hole in the tank for the fuel to expand into the overflow and get past a faulty check valve, it’s not impossible!!, seems unlikely but not impossible, as I said above I couldn’t understand why a faulty check valve on its own would lead to the leak (on a stationary bike) so maybe Rhubarb and Custard are correct and it a split or detached pipe, it’ll be interesting to see what the answer is!.
    UPDATE 3 ; Or is it 16cc :)
     
    #20 Mark9, Jul 17, 2020
    Last edited: Jul 17, 2020
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