On a recent trip from Minneapolis to Thunder Bay, I experienced something odd with my bike. (1991 K100RS 16v) After a brief rest stop, I noticed that the bike ran rough momentarily while entering the freeway, but things smoothed out by the time I merged into the 70 mph traffic. It lasted for only a few seconds and was over before I knew it. For the next 300 miles or so, the bike ran as smooth as always with no signs of trouble. On the trip back, I noticed that the bike slowly started to run rough, getting progressively worse by the time I got home. Fuel mileage dropped from 49-50 mpg to 38-40 mpg as well. It also seemed I caught a whiff of gasoline as it idled. I pulled the plugs and found that one was fouled. I installed new plugs and was unable to start or get the bike to run without holding the throttle open a bit. Blue smoke was visible and the bike backfired and stalled whenever I let off the throttle. Once warmed up, it will barely idle, with intermittent popping. I pulled the new plugs again and found the same cylinder appeared to be running much more rich than the others.
(The plugs were pulled after only about 5 minutes of running time). I haven't been home enough to dig into it too much since then. I've tried checking different posts here but either I haven't found or I've overlooked the answer. Anyone have any ideas? Fuel injector problem? Air leak from one of the rubber boots? Or something more sinister like a bad valve? One of the many tools I inherited from my dad was a compression tester but the thread size is too large for my K bike, so I haven't been able to check that yet. I was able to successfully rebuild the forks and do a spline lube this Spring - I'm just wondering how much work I may be in for now...
