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Thread: Removing air filter-1992 K-75RT

  1. #1
    Dale Rudolph
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    Removing air filter-1992 K-75RT

    The first and last time I changed the air filter on this bike, I also changed the fuel filter and anti freeze. Changing the anti freeze requires taking the tank off, which is why I didn't have any trouble getting the air filter out.

    I tried to get the air filter out of the air filter case today, but the upper part of the case will not lift high enough to pull the filter out. The owners manual says to release the three spring clips and lift the upper case to pull the filter out, the Haynes manual says to remove the tank.

    Has anyone come up with a way to get the filter out without removing the tank?

    My second question concerns whether leaving the "Choke" lever fully open for a month would have an effect on the bike now not starting? About 5 weeks ago, I changed the oil and ran the engine for a few minuets afterward. Between having surgery and bad weather, I just today tried to start it, this is the first time it has ever failed to very quickly start for me. Would having the "Choke" lever open for the last
    five weeks cause either flooding or allowing all the fuel in the injection system to evaporate? If this wouldn't having any effect on the bike not starting, I will check the fuel pump and plugs.

    Thanks for any suggestions.

  2. #2
    Benchwrenching PGlaves's Avatar
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    The "choke" is nothing more than a cable that pulls the throttle slightly open. It has nothing to do with the delivery of fuel whatsoever.
    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://www.bigbend.net/users/glaves

  3. #3
    Registered User
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    Air Filter

    The answer to your first question is "probably not". That also probably has to do with latching and unlatching those clips. I have two K100RTs and I check the filters every time I have the tanks off. The word there is Check. Check for butterfly guts and squirrel corn. You think I am kidding. Tap the filter on the bench a few times and replace the old filter. The 120k bike has had two filters one at 50k and one at 100k. Not because I thought they were plugged or not doing their job but because I thought they deserved them. K filters are way over capacity.

    The answer to you second question is a definate no. The Choke simply raises the idle ,opens the throttle, by two steps then falls back to one step. K75s do flood on occasion, if there is a slow start. Check the plugs for wet and if they are put in new dry plugs.
    Harold In Kansas
    1985 K100RT Bullit
    1985 K100XX/EML Bemel

  4. #4
    Dale Rudolph
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    Thanks for the replies.
    I took the plugs out, they were slightly wet, they only have about 2,000 miles on them. I dried and cleaned them, the bike started and ran very rough for about 5 seconds and would not re-start.
    I will drain most of the fuel out of the tank and see if just raising the rear of the tank will give me enough room to get the air filter out.

    While most of the fuel is out, I'll see if the pump works with the switch and if it does, see if fuel is reaching the fuel injection rail.

    Any suggestions on where to buy a fuel pump if that should be the problem?

  5. #5
    Benchwrenching PGlaves's Avatar
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    The plugs were "wet". Unless it was water, fuel is getting to the rail. If it was water it was the fuel pump that pumped it there from the tank.
    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://www.bigbend.net/users/glaves

  6. #6
    BMW uber alles! Zagando's Avatar
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    Airbox Wrestling 101

    The reason you will need to remove the tank is so you can stick a long flat-bladed screwdriver between the maze of wiring (underneath it) above the air filter box to loosen the cable clamp screw that clamps onto the plenum deep inside the "interior". While it may be technically possible to remove the air filter without doing so I rather doubt it would work without causing major aggravation.

    If you loosen the air filter top by undoing the three spring clips AND the plenum intake pipe then you can wiggle the top up and out enough to pull the air filter.

    It also helps to pull up on the wires above it to give it every possible fraction of a millimeter of much needed space, too!

    When you put the air filter back in remember to tighten the plenum pipe clamp before you put the tank all the way back on. Make sure that the filter orientation is correct (only one way it goes in) and it also helps to put a light coating of Armor All or Back to Black along the edges for lubrication.

    After doing this a few times you will get the hang of it and I assure you that removing the tank is dead simple by comparison. Getting those spring clips back in place is also quite tricky but a pair of long forceps (Harbor Freight $3) really makes it a lot easier.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  7. #7
    RK Ryder
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    I lift the back of the gas tank and insert a short 2x4, to hold the tank up about 4" and then slide out the old filter and then in with the new one.
    Paul
    Retired and riding my RTs, the '87 K100 & the '98 R1100 !
    Treasurer of the Forest City Motorrad Club #159
    Knights of the Roundel #333

  8. #8
    Dale Rudolph
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    I have to wonder if the "Wet", if it is water, is a result of ethanol setting in the tank for close to 2 months. I use both, a fuel preserative and an ethanol treatment.
    I drained most of the fuel out and took the fuel cap off the tank, with the switch on and touching the starter, I could hear the pump and also see fuel moving around in the tubing.

    I guess my next step will be to change the fuel filter, the local BMW shop is closed for the next week. I know there is a list of other filters that will work, any one of them more advisable than others?

    I remember the last time I took the tank off, the thing I had the most trouble with was the two brass clips that hold down the rear of the tank to the frame. They come out much easier than they go back in.

    Thanks for the opinions.

  9. #9
    RK Ryder
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    Quote Originally Posted by RUDYJO View Post
    I have to wonder if the "Wet", if it is water, is a result of ethanol setting in the tank for close to 2 months. I use both, a fuel preserative and an ethanol treatment.
    I drained most of the fuel out and took the fuel cap off the tank, with the switch on and touching the starter, I could hear the pump and also see fuel moving around in the tubing.

    I guess my next step will be to change the fuel filter, the local BMW shop is closed for the next week. I know there is a list of other filters that will work, any one of them more advisable than others?

    I remember the last time I took the tank off, the thing I had the most trouble with was the two brass clips that hold down the rear of the tank to the frame. They come out much easier than they go back in.

    Thanks for the opinions.
    NAPA Gold 3032 gas filter about $6
    Paul
    Retired and riding my RTs, the '87 K100 & the '98 R1100 !
    Treasurer of the Forest City Motorrad Club #159
    Knights of the Roundel #333

  10. #10
    Debbie's Servant Lee's Avatar
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    I'm guessing the RT has more stuff in the way. On our K75Ss I never had to lift the tank to replace the air-filter.
    Lee 2011 K1300S
    MOA # 30878
    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

  11. #11
    Rally Rat
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    The early hard-sided filter was very difficult to R&R. Later ones have a shorter lip on the left side. Once the clips have been popped off the filter slides in fairly easily.

  12. #12
    Dale Rudolph
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    Paul_F... thanks for the info on the NAPA filter, I'll see if they have one in stock.

    Lostboy + Lee.....As much as I like the RT model, the lower fairings come off for much of the maintenance work. After doing it so many times, it all comes off quickly.
    The thing that is preventing the filter lid from being lifted is the rubber gasket that runs all the way across the bottom of the tank, the lower part of the gasket is on the top of the frame.
    While the gasket does not sit on the frame in the middle, it does prevent the filter lid from being raised.

    Now that the fuel is out of the tank, I'll see if I can raise it enough to get a small 2x4 between the frame and tank which should allow the filter lid to lift, it only needs to come up about another 1/2 inch.

    This is the first time it has ever failed to start for me, if it had to happen, I'm glad it was in the driveway and not out on the road somewhere.

  13. #13
    Dale Rudolph
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    Yesterday I drained the fuel tank to make it easier to lift the back of the tank to get the air filter changed.

    This morning I thought I would try one more time to start it, it started right up with no hesitation.

    Does the fuel filter empty itself when almost all of the fuel is out of the tank? Could this be a case of water in the filter that was preventing the bike from starting?
    It is probably running on what was left in the fuel line and F.I. rail.

    I will change the fuel filter and fill the tank with non-ethanol gas. While I'm glad that it is running again, without really knowing why it wouldn't start , It leaves me a little uncomfortable taking it out again.

  14. #14
    Dale Rudolph
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    I got the air and fuel filters changed, both with no problems. I added 5 gallons of non-ethanol gas and the bike starts instantly as it always did.
    I am still convinced that the original non-starting problem was a result of ethanol gas being in the tank for almost 2 months. I will use only non-ethanol gas during the winter months when the bike tends to
    not get used often. Adding an ethanol treatment did not seem to prevent the water problem.

    Two comments; I removed the two rear clips on the gas tank and raised the rear of the tank to help gain more height. Maybe in different models or years, raising the tank may make it easier the remove the air filter, In my case, it made no difference. What I failed to notice when I first tried to remove the air filter is that after the 3 clips are released, the air filter pulls straight out. I originally thought that the filter was taken out only after separating the lower and upper halves of the air-filter case. It is not really nessesary to lift the top half of the case.
    What I now know is that when you look at the air filter case, it is not a top and bottom that needs to be separated to get the filter out, it is a top and bottom with the actual air filter being the whole middle
    one inch, the air filter does not rest in the case, the filter is the middle of the case. It seems simple now as to how it comes out, but as the top and bottom halves of the case and the filter itself are compressed together for years, they tend to become one solid unit.

    My second comment has to do with what hhshort mentioned.... these filters are made to last a very long time. As the old filter had been in the bike from the week that I bought it 5 years ago and had around
    nine thousand miles on it, I figuered it must need to be replaced. If I had known that the old filter was going to look like it had 100 miles of use and tapping it resulted in almost nothing coming out of it, I would
    not have spent the $41.55 for the new one. With the number of miles I use the bike a year, I don't think I'll ever have to change it again.

  15. #15
    A bozo on the bus deilenberger's Avatar
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    The K filter on the K75 is SO oversized for the engine displacement that even partly plugged it isn't going to be a restriction. The test for a restriction is a top-speed run. If plugged, the air-flow meter will automatically tell the L-Jetronic to dial back the fuel so the mixture isn't too rich (and your mileage doesn't drop off.)

    Clever part of the filter design is having the airflow from bottom to top.. most of the dirt (bugs, crap) that would normally accumulate in the filter is shaken out by intake pulses and ends up in the bottom half of the airbox. I always used a vacuum cleaner on that half when replacing (or simply checking) the filter.. be surprised at the amount of dead bugs that can build up there.
    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

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