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  1. #1

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    Ideas for new fuel tank vent.

    Im adding a 12 gallon tank to the rear of my ski for long trips. I have seen many setups but one thing I have not seen any good shots are of tank vent. The factory vent hole seems to small to fill the tank so I want to add a 3/8 fitting to the factory tank. What are some good setups to do this to prevent fuel leaks? Or is the factory vent hole adequate for the fuel transfer from the aux tank. This is for a 18 fxho.


  2. #2
    It wouldnt matter because the check valve on the vent is the small size. Also your engine wont pull more fuel then the vent will allow in. Lastly on the aux tanks tbm etc you attach the vent line from the main tank to the fuel outlet to the aux tank. This auto fills the main tank. Then the vent from aux tank to the main vent line venting the ski. The aux tank drains first into the main tank so your vent line will always allow air though from aux to main tank. Easy system works great no issues. The aux tank hads quick dissconnects. So when discconected all you do his unhook the vent line from aux and attach to vent from main and the system is back to stock. I use both ways all the time running high boost never had an issue!!

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  4. #3

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    I know how the lines hook up, but you can move more air through a 1/4” line then you can fuel due to resistance. When I hook the fuel line from the aux tank to the 1/4” hole on top of the fuel tank I was thinking there would be to much restriction. From what I’m reading is you use the 1/4” line on the main tank to fill it from the aux tank and have no issues? If this is the case I will try it that way first. Thanks

  5. #4
    MSX 150 guy lives on Mr. GP1800's Avatar
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    Myself and a friend have been discussing making this type of setup. The trick it seems is venting a modern external tank. The modern tanks are vented through the fuel cap and there is no vent fitting on them. How are people setting this up?

  6. #5
    Yes never had an issue. GP1800, dont know which ski you have but this is modern as it gets. All the skies have a vent line with a check valve from what I can see. Thats a 2019 parts diagram
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #6

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    Quote Originally Posted by Mr. GP1800 View Post
    Myself and a friend have been discussing making this type of setup. The trick it seems is venting a modern external tank. The modern tanks are vented through the fuel cap and there is no vent fitting on them. How are people setting this up?
    You can buy non epa Compliant fuel caps online then add a vent where ever you would like on the aux tank. I’m going to use a 90 degree barbed bulkhead fitting in the non epa fill cap.

  8. #7
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by scittb View Post
    Yes never had an issue. GP1800, dont know which ski you have but this is modern as it gets. All the skies have a vent line with a check valve from what I can see. Thats a 2019 parts diagram
    The question is about venting the external auxiliary fuel tank, not the OEM internal fuel tank.

    The project in mind is indeed for a GP1800 (2017). The EPA rated external fuel tanks have caps that do not release until something close to 5PSI. Initially there was concern that the sealed cap would also induce excessive vacuum as the fuel was drawn from the external tank.

    Further reading, however, suggests that the most recent Moeller external EPA rated fuel tanks have (or can have) a multi-mode cap that does allow vacuum relief as the fuel is drawn out.

    In support of the requirement for reduced fuel vapor from the vented cap on the tank, we had to source a newly designed cap from Kelch.

    The requirement states the following; the cap must have a tether, provide an audible click for closure, seal up to 5PSI out, allow vacuum in, an external or integrated means to temporarily relieve pressure within the tank prior to fuel filling or connection to the engine and a storage mode to seal the tank which will not allow the tank to vent.

    ... instructions; this will indicate how to relieve pressure prior to opening the cap or reconnecting the fuel line assembly to the engine

    Attachment 443340
    Point 4 suggests the vent cap does have ability to vent the tank when partial vacuum/suction occurs.

  9. #8
    Click avatar for tech links/info K447's Avatar
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    Kelch fuel tank caps

    https://www.kelch.com/products/caps-gauges-and-sensors/?custom_f_3%5B0%5D=436170&custom_f_4%5B0%5D=322031 2f3422202d204d6f64656c20323235&custom_f_5%5B0%5D=4 36f6e74726f6c2056656e74



    Attwood Sprayless fuel hose connector
    • Recessed check valves prevent spray when accidentally bumped.
    • Connectors designed to automatically seal if accidentally ripped apart.
    http://www.attwoodmarine.com/store/p...less-connector
    Last edited by K447; 01-06-2019 at 11:29 PM.

  10. #9

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    Quote Originally Posted by C42480 View Post
    I know how the lines hook up, but you can move more air through a 1/4 line then you can fuel due to resistance. When I hook the fuel line from the aux tank to the 1/4 hole on top of the fuel tank I was thinking there would be to much restriction. From what Im reading is you use the 1/4 line on the main tank to fill it from the aux tank and have no issues? If this is the case I will try it that way first. Thanks
    I was the one who sold those under the seat tanks for the fz skis for a while. I'd say 99.9% of people just used the 1/4" line with zero issues. Only person i know who used larger had 2 auxiliary tanks, mine under the seat and one on the back deck so his setup was obviously different

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  12. #10

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    Thanks for the ideas and information I appreciate it.

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