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Thread: 1994 K75S Unblocking a blocked tank vent?

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  1. #1
    BMW uber alles! Zagando's Avatar
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    Question 1994 K75S Unblocking a blocked tank vent?

    New problem:

    I believe one of my tank vent lines is blocked or somehow restricted. If so, it's probably what has been causing the high pitched chirping (subject of another current thread),

    I have tried blowing through a hose attached to the vent pipes protruding from underneath my tank. The rear one lets some air in but the forwardmost pipe is blocked.

    Anyone have any ideas on unblocking it?
    I already tried #12 gauge copper wire; it'll only go in about two inches before it must hit a sharp bend or something.

    I'm going to try blowing some air in with my HVLP turbine to see if that makes any difference (probably not but it's the only other idea I have at the moment.

    Help!
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

  2. #2
    3 Red Bricks
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    It's probably plugged with polishing compound.


    Use real compressed air (over 50psi). Remove the tank. You're going to have to clean out whatever you blow into the tank.

    The rear one is the rain drain for your cap. Open the cap while blowing through the rear tube. You should have air coming out a hole on the left side of the filler flange.

    The front one is the tank vent. Air should come into the tank roof area.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
    BMW uber alles! Zagando's Avatar
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    Polishing compound, ha ha. Good one, Lee.

    Btw, the tank is already off the bike while I replace all the hoses and install the new ABS relay, etc. and I haven't put it back on just yet. The winds turned into rain so I rolled the bike onto the porch to have some shelter. Now it is dark so I'll continue working on it tomorrow or the next day (might take a day trip tomorrow so maybe I'll have to wait until Sunday).

    Plenty of air comes out the little hole by the side of the gas cap when I put my turbine's nozzle on it, so no problem there.

    After trying heavy, stiff wire in the other front vent pipe I snaked in some very flexible PVC covered 18 ga. wire and got it all the way in (AFAIK)---a good 11" or so. Then I put the nozzle back up to the little pipe and it seems to have made a difference. The wire looked fairly clean when I pulled it out but maybe there was something in there that blocked it enough to prevent further air pressure ingress.

    Should there be any resistance at all or should the front vent pipe be just as unrestricted as the other already is?


    Either way, I'll take the gas cap off again and have a good look around inside the tank before proceeding further. I have some gas that I can put in the tank so as to slosh it around and see if there's any, uh, polishing compund or other crud floating around that needs to be evacuated.

    PS: Our housemate has an air compressor on hand so will try that if necessary---but maybe it's OK now (depends on the answer to my question above).

    Thanks, Lee!
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

  4. #4
    A bozo on the bus deilenberger's Avatar
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    I don't think it's a new problem.. Have you noticed a "whoosh" when you open the cap to fill up? That's the usual sign of a plugged up vent. As the gas is pumped out, and no air can get in, a partial vacuum is formed.. and the fuel pump has to work harder (causing it to chirp perhaps?)

    To clean out those sort of lines, it's hard to beat weed-wacker line.. it's thin enough to wind through, and thick enough and touch enough to not break. I used it on an '04 R1150RS I bought where the cap rain drain was completely plugged up.. and that drain for some bizarre reason ran a series of loops around part of the cap assembly, soldered in place. Weed-wacker got through, followed by compressed air, and finished up with WD40 (to try to protect it a bit..)
    Don Eilenberger http://www.eilenberger.net
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  5. #5
    3 Red Bricks
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    The plugged vent could very well be the source of your chirping noise. The pressure may have been releasing past the cap gasket. Chirp, chirp,chirp.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  6. #6
    Dum vivimus vivamus ted's Avatar
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    Maybe it is a cricket that is stuck in the vent
    Ted
    "A good stick is a good reason"
    1994 K75RT
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  7. #7
    BMW uber alles! Zagando's Avatar
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    Thumbs up Detective Superintendant K-Don

    Quote Originally Posted by deilenberger View Post
    I don't think it's a new problem.. Have you noticed a "whoosh" when you open the cap to fill up? That's the usual sign of a plugged up vent. As the gas is pumped out, and no air can get in, a partial vacuum is formed.. and the fuel pump has to work harder (causing it to chirp perhaps?)

    To clean out those sort of lines, it's hard to beat weed-wacker line.......
    Yes, I think you probably nailed it again, Don. Our housemate thought it also might be the source of the chirping problem and told me to open the tank the next time I heard it screeching to see if that made any difference. Believe I mentioned this in my chirping thread a few days ago but anyway I am guessing that your hunch/his hunch/my hunch is correct. I have almost always heard that whoosh every time I stop for gas and open the tank---so often that I thought it was normal!

    I think I still have some red plastic weed whacker line around here somewhere. Although my wife and I will probably be making a day trip tomorrow in another vehicle I may try to see if I can clear the vent before we leave. Then I would almost be assured of perfect performance or at least the bike would be a whole lot closer to normal than it's been for the nearly four years I've had it (Oct. 1st "birthday"). Will let you all know the outcome as soon as I can.

    It will be quite a relief to have the bike running well (poss. better) again and the fall riding season around here is nothing short of fantastic.
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

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