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Thread: Small internal tank hose purpose? (1987 K75C)

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  1. #1
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    Small internal tank hose purpose? (1987 K75C)

    Can someone explain the purpose of the small, 6mm tube in the tank, which goes from the side of the strainer basket to a short aluminum line at the top of the tank, just behind the filler cap? It's #15 in the attached image, which doesn't show the top attachment point.

    As best I can tell, it exists only to suck fuel from behind the baffle or plate at the top rear of the tank, but it seems to me that a hole at the bottom of said baffle would do just as well.

    On my bike, the aluminum tube to which the hose connects has broken free. My first instinct is to just remove the hose entirely. It's not present at all on the earlier bikes, and I've ridden without it before. On the other hand, it must have some good reason to be there, right?

    Perhaps relatedly, I've had a recurrence of the power loss issue described in this thread, which appeared to have been fixed about 2500 miles ago: http://www.bmwmoa.org/forum/archive/...p?t-65698.html. As I looked at the loose end of the hose waving around the tank this afternoon, it occurred to me that just maybe, under exactly the right circumstances, that hose could pull in an air bubble, that could be sucked into the fuel pump, which would cause something very much like I experienced.
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  2. #2
    Nick Kennedy
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    James
    I've got that same hose in my 1990 K75 tank and I wonder if it is the return fuel line from the fuel injection system and it is dumping fuel back in the tank at the bottom next to or under the strainer?..
    If you took you fuel cap off so you could see in there and started the bike, [ outside in case fuel started spraying around!] I wonder if fuel would be coming out of that broken off aluminum line you have...I don't think it is a fuel pick up..
    Any one out there know what the purpose of this little fuel line is?
    Nick Kennedy

  3. #3
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    No, it isn't the return line. If you look in the tank with the bike running and a relatively low fuel level, you can see the returned fuel entering at the front of the tank.

  4. #4
    A bozo on the bus deilenberger's Avatar
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    It's a vent hose for the fuel strainer on the bottom of the fuel pump. The purpose sort of eluded me.. but that's officially what it is.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  5. #5
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    Thank you. How very odd.

    It turns out not to be part of my power loss problem, which I'm back to thinking is something electrical in the fuel supply.

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