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Thread: 91 K75 massive fuel leak.

  1. #1
    Instigator cele0001's Avatar
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    91 K75 massive fuel leak.

    I was helping a friend yesterday with his K75.
    It was poring fuel from the bottom of the fuel tank somewhere. After some inspection we found that fuel sender is rusty and I am assuming that the leak is coming from it. Not from the o ring but actually leaking through the wire pass through on the sender plate. I will try to verify it today by testing the sender only. The tank is off the bike so I can take a good look. The rest of the tank looks beautiful, and sender is the only "service hole" on the bottom of the tank.
    Has anybody seen anything like this?
    While in the tank we discovered that the fuel pump is aftermarket, poorly fitted, and the fuel lines are almost done as well.
    Can anybody recommend a full meal deal for the fuel tank guts at a reasonable price.
    I am leaning toward euromotoelectrics fuel pump combo as seen here

    http://www.euromotoelectrics.com/BOS...576kitplus.htm



    Fuel sender is BMW only item @$130 (max bmw).
    Any input is greatly appreciated. I don't want to get in the tank anytime soon. I will be smelling like gas for the next month.
    I want to be unique, just like everybody else.

  2. #2
    #13338 PGlaves's Avatar
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    Empty the tank. Put the tank somewhere where you can observe the bottom of the tank in its normal orientation. Fill the tank with water or some other non-flammable/explosive liquid. Observe the leak.

    Some of these tanks have rusted through at the low spot on the forward left side of the tank where water will settle when the bike is parked. Check there.

    I agree that Euromotoelectrics is where to go for the pump.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
    Instigator cele0001's Avatar
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    Quote Originally Posted by PGlaves View Post
    Empty the tank. Put the tank somewhere where you can observe the bottom of the tank in its normal orientation. Fill the tank with water or some other non-flammable/explosive liquid. Observe the leak.

    Some of these tanks have rusted through at the low spot on the forward left side of the tank where water will settle when the bike is parked. Check there.

    I agree that Euromotoelectrics is where to go for the pump.
    Thanks for the reply. I am aware of the front left area tank leak, (my RT had it), but it would be easy to spot since the paint would be coming up where the leak is.
    In this case I see nothing, from inside or outside of the tank. Also looking from the bottom I see no evidence of fuel on the underside except in the area lower than the sender plate. I will do the water test this afternoon. It is just strange.
    I think he is looking at $500 worth of parts either way, but he wants to keep the bike so lots of time to amortize the costs.
    I want to be unique, just like everybody else.

  4. #4
    #13338 PGlaves's Avatar
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    Quote Originally Posted by cele0001 View Post
    Thanks for the reply. I am aware of the front left area tank leak, (my RT had it), but it would be easy to spot since the paint would be coming up where the leak is.
    In this case I see nothing, from inside or outside of the tank. Also looking from the bottom I see no evidence of fuel on the underside except in the area lower than the sender plate. I will do the water test this afternoon. It is just strange.
    I think he is looking at $500 worth of parts either way, but he wants to keep the bike so lots of time to amortize the costs.
    There is either a flat gasket, or I think an O ring that seals that plate. Maybe?? Or does it seem to be flowing where the wires pass through??
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  5. #5
    Instigator cele0001's Avatar
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    The O ring looks intact. There is no evidence of a leak and it started leaking suddenly, and a lot. It leaked about 1/2 gallon in a 12 hour period.
    That is why I believe the only place left is the wire passthrough on the plate. Paint is peeling on the bottom of the tank only in the area lower than the plate but nothing around the O ring. If my assumption is correct, it is coming out under the white cap on the plate wiring and dripping down the wire harness onto the heat reflective liner and continuing lower. I will try to post some pictures later.
    I want to be unique, just like everybody else.

  6. #6
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    My father just had that O-ring under the sending unit leak. (Or that's what we are testing now) It went from a perfect seal, to leaking out the ~4 gallons over the weekend. For others and maybe the OP, I found it was easiest to take off the two small wires from the sending unit to the fuel pump, then the 4 screws holding the sending unit to the tank, and fish the old/new o-rings out/in. You don't actually have to remove the sending unit itself to replace the o-ring.

    It seems that leaking gas tanks are becoming more of a problem as the bikes age. I remember Paul G. saying that he will run some Isoheet (red bottle) though his K tanks to remove the water (which I would imagine would also reduce the likelihood of water eating through the tank in the low spots)

    Good luck!

  7. #7
    3 Red Bricks
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    EuroMotoElectrics is an excellent supplier of fuel and electrical items for our bikes.

    But, personally I would not go for the 52mm pump kit for two reasons. One, cost. Two, the 52mm pump uses a VERY fragile intake filter screen. BMW changed to a 43mm pump with a very robust sock style intake screen in Jan. of '93. A large amount of auto and aftermarket pumps use this style of screen (must be for a reason).

    It sounds like the only complaint with the current pump is that it does not mount correctly. Measure the pump diameter (I'll bet it's 37mm). If the original 52mm pump mount and vibration damper are still there and in fair condition (not dissolving or mushy) all you need to do is buy: http://www.euromotoelectrics.com/BMW...fp-576foam.htm

    If any other pieces are bad, just buy those from EuroMoto Electrics.

    If the pump is bad or you just want a new one, use:http://www.euromotoelectrics.com/BMW...231kitplus.htm
    This kit comes with a foam adapter to adapt to 43mm pump mount. Call them and see if they will substitue a foam adapter for the 52mm mount or just buy the adapter sepatately.

    I've had these pumps in two bikes for over 8 years and 80,000 miles with no issues.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  8. #8
    Instigator cele0001's Avatar
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    Good info. Thanks Lee.

    EDIT: Good call on the diameter issue. I wanted to go back to OEM but you are right, at $200 savings I will take your suggestion. Dampener is a little soft but not dissolving yet, so I might keep it. $57 for a piece of rubber is a little excessive (although a bargain comparing to BMW dealer prices).
    So I will go with new foam sleeve to make the pump sit better, new plastic ring to make it lock nicer, new lines, new filter and new sender unit. I should be able to get by for under$200. Pump is running fine and it is not difficult to get it out later (famous last words) so I will leave it alone for now.
    Last edited by cele0001; 03-19-2015 at 02:44 PM.
    I want to be unique, just like everybody else.

  9. #9
    3 Red Bricks
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    You might want to consider a used sending unit and take that savings and buy a new vibration damper.
    If the damper is softer than a tire or if it transfers a stain to your finger while it is submerged in fuel, it is puting crud into your fuel, pump, filter, and injectors, and it will only get worse.

    A good used sender is no worse than what every other bike out there is currently running (but use a new o-ring). PM me if you want me to check my sources for one.I would need the build date of your bike or the last six of the VIN.




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  10. #10
    Instigator cele0001's Avatar
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    Pm sent
    I want to be unique, just like everybody else.

  11. #11
    Still plays with trains. tinytrains's Avatar
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    Just a note on the used sender. My1988 K75 developed a bad sender unit. The fuel pump connection would open when it got hot and shut off the engine. Not saying not to buy a used one, but the do age.

    I had to replace the sender and pump damper for about $200. Can't complain though, that bike has cost very little in maintenance over 25 years.
    1988 K75 Low Seat
    2009 R1200R Roadster

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