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Thread: Using vent hose from fuel tank

  1. #1

    Smile Using vent hose from fuel tank

    I have an 03 r1200cl with a Hannigan sidecar. I replaced the right saddlebag with a 3gal. Rotopax. I used the tank vent that used to go to the charcoal canister to connect the Rotopax to the fuel tank. It seems to work fine the vacuum from the tank pulls the fuel from the cell into the tank as it is being used. After the bike is shut off you can hear fuel trickling into the tank as there is still vacuum present. This leads me to believe that the bike is using fuel faster than it is being transfered. The Rotopax is vented to atmosphere. Does anyone know if pulling full from the back of the bike will put extra strain on the fuel pump and cause problems with it in the long run. Thank you in advance.

  2. #2
    The tank vent has a built-in rollover valve, the orifice of which was sized to flow the right amount of AIR to keep the tank from building vacuum. That means that the orifice is too small to flow the same cc/min of FUEL. So, vacuum build is the result. How much it builds depends on your rate of fuel use and time. It is possible if you run fast enough and long enough that you will implode the tank. Most likely starving the bike for fuel or imploding the tank will happen before you damage the fuel pump. When I converted my R1150 and R1200's to vent fill from a permanently mounted auxiliary tank, I removed the rollover valve from the tank and replaced it with one in the aux. tank. After that the main tank did not build vacuum and when the aux. tank was empty, the main tank vented through it. I would only use this solution for a permanently mounted auxiliary tank - not a portable or temporary one.

    You say that the Rotopax is vented to atmosphere, does it have a rollover vent? If not, you might have created a potential danger in a crash or upset situation.

    Here are some pics from the R1200 FYI...

    This shows the rollover valve on the R12GS

    DSC05650-M.jpg

    You can see on disassembly that the vent orifice is small. Maybe it could be enlarged while still keeping the valve, but I did not try. That would be one way to reduce the vacuum level in the tank and speed up the fluid flow.

    DSC05652-M.jpg

    With the valve removed the fill neck was reinstalled. The thin vent hose was replaced with fuel injection hose...

    DSC05653-M.jpg

    Finished installation of aux. tank. It has two (redundant) NHRA approved rollover vent valves in it.

    DSC05655-M.jpg

    Before the permanent auxiliary tank I used a RotoPax, but I would not have attempted to plumb it inline...

    DSC05295-M.jpg
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  3. #3
    Registered User slime's Avatar
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    Do all BMW bikes have that vent check valve?

  4. #4
    Day Dreaming ... happy wanderer's Avatar
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    This is the Oilheads forum. This post needs moving to the Camheads/Hexheads forum where you can get answers from 1200 owners.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  5. #5
    Debbie's Servant Lee's Avatar
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    Quote Originally Posted by happy wanderer View Post
    This is the Oilheads forum. This post needs moving to the Camheads/Hexheads forum where you can get answers from 1200 owners.
    The Op has a R1200CL. I think that model is a Oilhead.
    Lee
    2016 R1200RS
    MOA # 30878
    Past BMW Bikes: 2011 K1300S, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

  6. #6
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by Lee View Post
    The Op has a R1200CL. I think that model is a Oilhead.
    Oooops. Saw the 1200 and photos of a 1200 and assumed it was a 1200. My bad! Yeah the cruisers are oilheads though!
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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