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Thread: 1994 K75S Unblocking a blocked tank vent?

  1. #16
    ...never too much lefse sleeper's Avatar
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    Quote Originally Posted by Zagando View Post
    I can't imagine what is blocking the vent so strongly, either. Thanks again, Jeff
    Is this the same tank you had repainted in a much earlier post? If so, could the blockage have originated during the prep/paint process?
    Robert Horton
    95 K75RT

  2. #17
    Dum vivimus vivamus ted's Avatar
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    Quote Originally Posted by Themason View Post
    I wonder if a gun cleaning brush can be shoved up to the blockage and used to whittle away at it?
    That is a great suggestion, I bet one of the flexible rods used for cleaning fixed-breach rifles with a brass brush would work, maybe in .22 caliber?

    Maybe fill it with carb cleaner then slowly, gently and carefully work at it with the brush?
    Ted
    "A good stick is a good reason"
    1994 K75RT
    Moto Pages

  3. #18
    BMW uber alles! Zagando's Avatar
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    Quote Originally Posted by sleeper View Post
    Is this the same tank you had repainted in a much earlier post? If so, could the blockage have originated during the prep/paint process?
    Didn't repaint the tank, I stripped, sanded and polished it (hence Lee's polishing compound joke earlier). Anyway, I've always been careful not to get anything in the tank that doesn't belong there in the first place.

    I wonder if the corrosive atmosphere and continually high humidity of my previous environment might have been a factor?
    ---Jeff '94 K75S Berlina

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

  4. #19
    BMW uber alles! Zagando's Avatar
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    I like 42906's and Ted's ideas of using a gun cleaning brush along with the carb cleaner, but I'm concerned with actually getting the brush to the gunked up area.

    According to Lee's earlier description it must be in the area that is not reachable from either side. If I read his post correctly, I hit the tank top (or plate) eventually (around 11' in (coming in from the bottom pipe---and I hit the top again (about 1-1.5" in) coming in from the in-tank little pipe that is the beginning of the vent.

    Unless one of those gun brushes is super flexible and able to get around a sharp bend or right angle I would think that the carb cleaner is my only realistic hope.

    Thanks for the basically brilliant ideas nonetheless; I may try the gun brush anyway if they're not terribly expensive.

    Now that I'm back from a dozen errands with carb cleaner in hand I'll get to injecting a healthy quantity into the vent pipe from the underside of the tank (which will be upside down, of course).
    ---Jeff '94 K75S Berlina

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

  5. #20
    BMW uber alles! Zagando's Avatar
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    Thumbs up Tank vent now UNBLOCKED!

    Before I even got the carb cleaner out my housemate suggested trying compressed air once more.

    Like the stuck jar lid that just won't budge until you hand it over to someone else to try, a single blast from his air compressor and air came gushing out from where the tank vent plate is!

    Still don't know what was causing it and there doesn't appear to be any crud in the tank now, either (except for a few very tiny specks in the otherwise CLEAN tank.

    I'm too relieved to bother with those little specks so I'll refill it after it's back on the bike.

    I'll need to take the tank off again soon once I have the fork work done so I can reattach all of my driving lights (removed them so my $95/hour mechanic won't have to deal with them when he's doing the important stuff that I cannot). I can siphon and clean the tank at that time if need be.

    I'll post a followup once everything is back together and I've done a good test ride to confirm.

    ---Finally a happy camper Thanks guys!
    ---Jeff '94 K75S Berlina

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

  6. #21
    A bozo on the bus deilenberger's Avatar
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    Jeff,

    I was puzzling what would cause a chirping noise if the tank went under vacuum. A vacuum would pull the cap seals closed even tighter, so I doubt if that would be it..

    Then a thought came to me (always dangerous..) - the high-pressure blowoff on the fuel pump is looking at "differential pressure" - ie - the difference between the input pressure and output pressure. When that differential pressure exceeds the force of the spring holding the blowoff closed, it opens and relieves output pressure.

    In this case - the input pressure is the pressure in the tank. If your vent is clogged up and you're pulling a vacuum on the tank, that means the input pressure is negative, so the blowoff will start opening at a lower output pressure. Combine that with a partly plugged fuel filter - and it becomes obvious to me what is happening.

    I suspect you'll be happy once you get your ride in
    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

  7. #22
    BMW uber alles! Zagando's Avatar
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    Talking Brief test ride; so far VERY GOOD!

    Late last night I rode a few miles on the freeway (60-70mph) to pick up my wife from work. On the way home we rode along the boulevards around 30-50mph and the bike seems noticeably smoother than ever before.

    I think the combination of unblocking the vent, new crankcase breather hose, new fuel injector nipple caps and 5 other new fuel/vacuum hoses really made a significant difference.

    Although I probably still need to get the valves adjusted the bike is now running better than ever. Now I finally know what others mean about the smoothness of the K75---nearly four years since I bought the bike!

    Don, your explanation makes perfect sense and I also suspect that the chirping is gone for good. I'd be surprised if it started again.

    The other good news is that my ABS system is back on AOK; the new ABS relay and a couple attempts to reset the brain took care of the warning lights staying on all the time.

    Now I can't wait to take her for a nice long ride!
    ---Jeff '94 K75S Berlina

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

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