fuel overflow problem
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  1. #1
    Newbie
    My Bike(s)
    Suzuki c50t
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    12

    fuel overflow problem

    Maybe someone can point me in the right direction. If I fill the tank up to the point where fuel is in the filler tube(not to the point of overflowing but just inside the tube extending downward from the top of the tank) and then start riding, in a mile or so fuel starts running out underneath the cap. I hav e stopped at this and turned off the engine,opened the cap and fuel continues to come out of the tank as if the tank is pressurized. What can be pressurizing the tank? Any ideas why this is happening . A local mechanic told me this can't happen but I see it ever time I fill the tank if its too full.

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  3. #2
    Newbie
    My Bike(s)
    Suzuki c50t
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    12
    Another question. Can anyone tell me if the fuel cap on a 2007 c50t is vented or not? This tank was sealed by a shop prior to my purchasing it. I was wondering if the cap vent(if there is one) could have been sealed by accident while the tank was being sealed. If the cap is supposed to vent but is not it could explain why the tank is pressurizing but not the source of the pressure. thoughts?

  4. #3
    Super Moderator

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    Can-AM Spyder
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    Quote Originally Posted by Learpilot View Post
    but I see it ever time I fill the tank if its too full.
    If it hurts when you do that, stop doing it !! (old joke)

    The recommendation for tank filling is the same for most all bikes: Fill it until the gas just barely TOUCHES the bottom of the filler tube....not IN the tube at all.

    The tank will naturally become slightly pressurized as the fuel heats up and the vent, wherever that is, should release a tiny bit of AIR to prevent that pressure from becoming too high.

    IF you actually are overfilling the tank, by the above standard, then some fuel spilling out the vent should be expected. In most cases, that vent is in the cap. I don't know about your particular model though. Someone else here likely will know.

    In the meantime, stop filling the tank so full.
    Don't believe everything that you think.

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  6. #4
    M-J Lifetime Achievement Award
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    Other than over filling I would suspect the venting system has been compromise with the sealing...a tank will leak a little fuel if over filled but not continue to do so once the cap has been opened unless the tank is pressurised....but even under normal 'fuel pressurising' due to heat the fuel should not flow out of the filler.

    Does it pressurise if only half full?...do you hear a hiss when undoing the tank cap. On some cars if the tank is almost empty it hisses but this is from a slight vacuum...not to be confused by an expelling of air....and in your case fuel. Does this bike have any kind of warranty? if so take it back to them for an inspection.

    If this bike has a fuel vapour recirculation system it may be clogged or the charcoal cannister relief valve may not be working or have a crimped pipe.


    Good luck

    Ps I seem to remember another similar incident reported on here with the same bike....you may be able to search for it and find a solution there.
    Last edited by Aussie Steve; 12-31-2017 at 09:01 PM.
    Smoke me a kipper I'll be home in time for breakfast

  7. #5
    Newbie
    My Bike(s)
    Suzuki c50t
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    12
    The earlier instance was me, I posted it last year but the problem is still there. If you look at my previous post you will see that the tank does not pressurize or over flow when the cap is off nor does the fuel get noticeably warmer while the engine is running. As stated before I have seen fuel flow out of the top of the filler hole with the cap off and engine stopped. This Bike is not a california model so no vapor canister.

  8. #6
    Super Moderator

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    Quote Originally Posted by Learpilot View Post
    The earlier instance was me, I posted it last year but the problem is still there.

    As stated before I have seen fuel flow out of the top of the filler hole with the cap off and engine stopped.
    So.....for the sake of clarity and continuity.....it would have been MUCH better if you had continued your original thread instead of starting a new one.

    Assuming that second statement is true as written, there are only two likely causes:

    1) The tank is WAY over filled
    2) You have an exhaust pipe or an exhaust leak heating the bottom of the tank or petcock or fuel line causing the gas to BOIL and vaporize at that point.
    And yes that can happen while the rest of the tank and the top of the gas still feels relatively cool.
    Don't believe everything that you think.

  9. #7
    M-J Lifetime Achievement Award
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    Does the bike have a fuel pump and if so is the return pressure above spec....cant think why it would be, but that would be a way the tank could get pressurised. Is there a hiss of escaping air if you pop the cap while it is overflowing. Is the fuel line free and not kinked or otherwise compromised.

    Is the bike a carb model or FI and if FI are the injectors free flowing any clogging may cause back pressure. Also is there a check valve between the injectors and the fuel pump that is inoperative and or kinked line.

    A way to check whether it is the tank or somewhere else would be to fit an auxiliary fuel supply and see if that pressurises. This would be difficult if the bike has a pump and FI.

    Good luck
    Smoke me a kipper I'll be home in time for breakfast

  10. #8
    Ditch Magnet
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    Brisbane Australia
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    I owned the 07 M50 and the fuel cap was vented. I never had a issue with fuel overflowing/leaking even when overfilling by 1-2L. (after level reached bottom of filler tube.) I suspect the cap vent is blocked which from memory is located under the locking lug assembly.

  11. #9
    Super Moderator

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    Quote Originally Posted by falcon View Post
    I owned the 07 M50 and the fuel cap was vented. I never had a issue with fuel overflowing/leaking even when overfilling by 1-2L. (after level reached bottom of filler tube.) I suspect the cap vent is blocked which from memory is located under the locking lug assembly.
    Good information.
    But with all other things being "normal", the tank should NEVER act like what he is describing.
    Fuel continuing to "boil" out after the cap has been opened indicates a much bigger problem than just the cap vent.
    Don't believe everything that you think.

  12. #10
    Newbie
    My Bike(s)
    Suzuki S83
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    3
    Something very close to this happened to me.

    For me, it was the clogged jets within my carbs. I know this is a long shot, but hope this helps

  13. #11
    Super Moderator

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    Quote Originally Posted by plee1224 View Post
    For me, it was the clogged jets within my carbs. I know this is a long shot, but hope this helps
    Are you really saying that something clogged inside the carbs caused the gas tank to become pressurized and spew out fuel ??

    I really doubt that.

    More likely that you solved the real problem somewhere else just by taking the fuel delivery system apart and putting it back together.
    Don't believe everything that you think.

  14. #12
    M-J Lifetime Achievement Award
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    I'm with ER on this... clogged jets would not cause the fuel tank to pressurise the bike would just refuse to run properly or at all. Even with a fuel pump once pressure reaches spec it switches off.
    Smoke me a kipper I'll be home in time for breakfast

  15. #13
    Ditch Magnet
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    CBF600SA
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    Nanaimo, BC
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    Learpilot, where are you located? Are you filling up the tank to the max in hot weather, on a hot bike?


 

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