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Thread: 85 K100 sputtering/backfiring/running rough

  1. #1

    85 K100 sputtering/backfiring/running rough

    So this post will be missing some information simply because there are several things I'm not sure of. Bought an 85 K100 off a friend who purchased it a year ago. It had been converted into a cafe racer and has no guages whatsoever. He rode it for a few months and let it sit for roughly 9 months out in the elements. I got it off him, drained gas tank, added new gas and fuel injector cleaner and got it started and running well, firing on all cylinders. Was a bit of delay under sharp acceleration but otherwise it ran strong and got to speed very quickly. Went around the neighborhood on short rides, 15-20 min and all was well. Then after replacing the rear master cylinder I took it on a longer ride, roughly an hour. Was running great and then towards the end it started running rough, backfiring a bit and sputtering. Got it home and changed the plugs and fuel filter so far with no effect. Have a compression tester coming but I don't suspect that's the problem. It starts and runs fine but runs rough. Far from scientific but all 4 pipes get hot so I don't suspect a dead cylinder. I know there's a big lack of info but just hoping someone has had something similar happen and can give me some ideas.

  2. #2
    Registered User GTRider's Avatar
    Join Date
    Apr 2006
    Nibley, UT USA
    Id start by replacing the fuel filter inside the tank.

    1983 R80ST 1984 R80 G/S PD 1993 R100GS 2004 K1200GT w/Hannigan S/C 2010 K1300GT
    BMWMOA#52184, AMA#271542, IBA#138

  3. #3
    I know you guys have been on the edge of your seat waiting for an update. I'm sorry to have kept you waiting but I return with good news. After changing the fuel and air filters along with spark plugs, taking apart and cleaning every connection I could find, compression checking each cylinder and checking fuel pressure I randomly happened to come across a vacuum tube that was cracked on the end and had come off. Was checking the fuel injector connections and my hand swiped across the tube that had come off. Pure chance but I've learned quite a bit about this motor along the way. So y'all can breathe now, all is well

  4. #4
    Registered User drneo66's Avatar
    Join Date
    Jun 2009
    Rochester, MN
    Current: 2007 BMW R1200RT
    Former: 1995 BMW K75S, 2009 BMW G650GS
    MOA Member #:150400, IBA#: 37558

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