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Thread: 1994 R1100RS Fuel pump questions

  1. #1
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    1994 R1100RS Fuel pump questions

    Been riding Harleys fo 30 years, and just picked up my first BMW. 1994 R1100RS with 17k miles and full service records. I bought this in time to make the rally in Great Falls. Had new tires installed and the 18k mile service done before the trip. Everything went great! 1700 miles no problems. Then last week, the bike started hard. Then ran rough all the way home. It won't rev above 4k rpm. Checked fuse 6 and swapped the relay, all ok. When turning on the ignition, I can hear the pump pulse, and fuel returning to the tank. But when the engine starts, I can't hear the pump running in the tank. With the engine running, should the pump run continuously? Like I said, everything was fine since June until last Friday. It has only had non ethanol gas since new. I love this bike, but could use some help. Could it just be a fuel filter?
    Last edited by boiserider63; 09-24-2021 at 03:51 AM.

  2. #2
    #13338 PGlaves's Avatar
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    The pump is hard to hear when the engine is running. But, your symptoms do suggest a clogged/clogging fuel filter.
    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/

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    Thats what I was thinking. I bought a new pump, filter lines and quick disconnects. Might as well do the whole job while I'm there. Thanks for the input. Will let you know the results this weekend.

  4. #4
    Gerard jagarra's Avatar
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    Another thing to check after you remove the access to the tank, there is a vibration damper inside the tank for the fuel pump. When I bought my RS, it too had disintegrated over time. Just another thing to clog the pick up.
    1994 R1100RS-(5/93)-,1974 R90/6 built 9/73,--1987 K75S,--1964 Triumph T100--1986 Honda XL600R

  5. #5

    Check the Hall sender connection

    While you have the gas tank off check the wire insulation and connection for the hall sending unit (ignition & fuel pump control). If the insulation is cracked or there are bare wires it needs to be addressed. Theres a member on this forum that can rewire it or you can buy a new one if needed.

  6. #6
    Neglected Bike Adopter
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    Ditto on the Hall Sensor check. Every single one of them prior to a certain build date fails eventually due to the incorrectly-specified factory wiring. Even if it doesn't fix your hard starting problem now, it will be a problem later if it isn't addressed.
    GSAddict on this forum is the guy you want to talk to if yours needs rebuilding. He guarantees his wiring repairs with a lifetime warranty.

    I agree with PGlaves; the symptoms you describe certainly sound like a clogged fuel filter.

    After you put that mileage on the bike, did you notice any increase in fuel pump noise from when it was starting previously? Normally an obstruction in the fuel system can cause a factory pump to make a bit more noise than typical. However, this is difficult to know if you aren't very familiar with exactly how the fuel pump sounds normally, and the fuel pump sound level also varies based on how much gas is in the tank.

    It's possible that you got one batch of properly bad gas and that clogged up the filter. Sometimes it happens.
    Owner of the saddest 1997 R850R you ever did see.

  7. #7
    When I replaced the fuel filter (not pump!) on my 94 R1100RS for the first time it was a bit of an adventure.

    It would be worthwhile to have on hand new o-rings that fit around the fuel filler cap and around the fuel pump access port. You may not need these o-rings, but if you don't have extras on hand, then you surely will need them!

    One should siphon as much gas as possible from the tank prior to removal from the bike. There are four hoses to disconnect from the tank; two are vent hoses and two are fuel hoses. BEFORE disconnecting the rubber fuel lines from the hard plastic lines to the fuel injectors I place clamps over the rubber hoses (to keep that remaining fuel in the tank from leaking). An image of the clamps that I use is shown below with a link from the 'zon (these clamps are likely available at many other locations).
    https://www.amazon.com/OTC-4506-Fuel...%2C203&sr=8-13

    Disconnect the electrical connection to the fuel tank and all fasteners to the fuel tank.
    I place the removed fuel tank on its side on a towel on a piece of cardboard on the garage floor. Best to to this in a well-ventillated area; smoking and sparks are ill advised.

    I remove the fasteners securing the cover over the fuel pump access port in a cris-cross manner (these are re-secured in a similar manner; very little torque is needed on these fasteners).

    Prior to disconnecting the vent hoses from the cover (which go to the fuel fill cap) I place some wire about the hoses. If the hoses are pulled from the fill cap; one will most likely need the o-ring for the fill cap as the fill cap will need to be removed to re-attach the vent lines.

    Removal of the fuel pump - filter assembly is a bit tricky. There is a good deal of rotation and translation involved; sort of like fitting a five-gallon bucket in a three gallon pail! Take care with the coarse screen at the intake. I managed to damage this screen on my first attempt. (A staple gun might be useful in making a repair to the screen or replacement of the screen could be necessary).


    As I recall BMW uses Oetiker-type "pinch" clamps on the internal fuel lines. I dislike these one-use clamps, but others may enjoy the removal and installation of new Oetiker clamps. (An image of these type of clamps is shown along with a link from the 'zon).
    https://www.amazon.com/125PCS-7-21mm...2482813&sr=8-6

    I replace the Oetiker clamps with re-usable clamps made for fuel injection (i.e., pressurized) fuel lines. It is not recommended to use the worm-screw type of radiator hose clamps that are less expensive. (Images and links are shown for both types).
    https://www.amazon.com/Glarks-14-16m...s%2C203&sr=8-7
    https://www.amazon.com/TICONN-60PCS-...s%2C203&sr=8-5

    Some folks so dislike the process of replacing the fuel filter that they have moved the filter external to the fuel tank for easier access. Further discussion of this may be found on the IBMWR.org tech pages.
    https://ibmwr.org/index.php/2000/06/...-modification/

    fuel line clamp.jpg

    pinch clamps.jpg

    fuel injection clamp.jpg

    worm gear clamp.jpg

  8. #8
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    Thanks for all the tips. I will start the job tonight, and post the results.

  9. #9
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    Quote Originally Posted by robsryder View Post
    Some folks so dislike the process of replacing the fuel filter that they have moved the filter external to the fuel tank for easier access.
    Be warned that if you do this there is quite a risk involved, and it's your call whether that risk is worth it.

    BMW put the filter in the fuel tank for a very good safety reason. It is possible that when the fuel filter clogs up very badly, the pressure inside the fuel filter can go far higher than it's designed for and the filter can burst. If this happens on a running bike with an external fuel filter mod...well, you can imagine what happens when gasoline hits a hot engine.

    Chris Harris, the former-professional BMW mechanic who for years posted excellent maintenance videos for Oilheads and Airheads on Youtube, said in a video that he personally saw two burned-up bikes because of burst external fuel filters.

    It probably wouldn't be an issue if the filter were replaced on an accelerated schedule, every 12k instead of the manual's specified 24k, but you should know the risk is there.
    Owner of the saddest 1997 R850R you ever did see.

  10. #10
    MOA #24991 Pauls1150's Avatar
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    My external fuel filter is the WIX p/n 33032, UPC # 765809330320. This is used as an acceptable replacement for hundreds of vehicles, including little cars, big cars, and construction equipment.
    See - https://www.wixfilters.com/Lookup/Pa...spx?Part=33032
    If it had problems, we'd have heard about it...
    Note that there is also a filter on the pump's intake side that requires periodic renewal.

  11. #11
    #13338 PGlaves's Avatar
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    Quote Originally Posted by Pauls1150 View Post
    My external fuel filter is the WIX p/n 33032, UPC # 765809330320. This is used as an acceptable replacement for hundreds of vehicles, including little cars, big cars, and construction equipment.
    See - https://www.wixfilters.com/Lookup/Pa...spx?Part=33032
    If it had problems, we'd have heard about it...
    Note that there is also a filter on the pump's intake side that requires periodic renewal.
    In the early days of yore - K100, K75, K1100 - and then with the early days of Oilheads, the BMW OEM fuel filters had crimped, not welded, filter bodies. The OEM placement was inside the tank. There were numerous failures when these filters burst at the crimped seam, often for no apparent reason.

    The K bike filters are easy to change, even beside the road. They are accessed through the top of the tank by removing the filler cap assembly. The Oilhead filters are a lot more trouble to replace. They require removing the fuel tank, emptying the fuel tank, laying the fuel tank on its side, and fishing 6 inches of stuff through a 4 inch hole. Not fun in the dirt beside the road with a painted R1100RS or R1150R tank. And then to put it all back together usually requires a new O ring to seal the pump plate to the tank because the old O ring has swelled.

    So, I never bothered to put an external filter on a K bike. And I would never put an OEM crimped filter external to the tank because of their failure history. But on Voni's two R1100RS bikes and my R1150R bike I did move the filters to a location outside the tank. I used the WIX welded body filters mentioned above.

    The first bike I did this to was Big Red, Voni's venerable R1100RS back when she was riding solo, by herself all over the US and Canada - riding 73,660 miles mostly by herself in the 1999 six month BMW MOA mileage contest. She of course knew how to change out the filter with the spare in the tailcone, if need arose.

    While an OEM pump is capable of splitting a crimped seam on an OEM filter I don't think an OEM pump unregulated at full tilt boogie has enough pressure to split a welded seam WIX filter. We never had an issue with the external filters during about 600,000 miles of riding.
    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/

  12. #12
    Neglected Bike Adopter
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    Makes sense that a stronger fuel filter would be a good fit for that mod. That sounds like a much diminished risk to me.
    Owner of the saddest 1997 R850R you ever did see.

  13. #13
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    Removed the fuel tank and got the fuel pump assembly removed. Fuel filter was completely clogged! Re-assembled with new pump, filter, and lines from Beemer Boneyard. Also replaced all vent lines and external fuel lines as they were rock hard after 27 years. Bike fired right up and runs great. Thanks for all the advice, I really appreciate it!

  14. #14
    #13338 PGlaves's Avatar
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    Quote Originally Posted by boiserider63 View Post
    Removed the fuel tank and got the fuel pump assembly removed. Fuel filter was completely clogged! Re-assembled with new pump, filter, and lines from Beemer Boneyard. Also replaced all vent lines and external fuel lines as they were rock hard after 27 years. Bike fired right up and runs great. Thanks for all the advice, I really appreciate it!
    Excellent! Thanks for letting us know the results.
    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/

  15. #15
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    Quote Originally Posted by PGlaves View Post
    Excellent! Thanks for letting us know the results.
    +1



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