While lubing the splines this weekend I took the opportunity to do some other maintenance work which included changing the fuel filter. First thing I found was the outlet hose was cracked and had some of the outer rubber flaking off. I also noticed black stuff through the inlet tube on the filter. After I put everything back together I fired my K75 up and noticed it was running slightly smoother at idle. That, along with the black junk in the inlet tube, prompted me to cut open the old fuel filter to see what was inside.
Here's what I found.
The brown red stuff in the can on the last photo is powdered rust.
Yesterday I went on a 130 mile road test. Not only is the engine smoother with less vibration at all speeds but it had better throttle response especially in 5th gear in 55mph to 85mph acceleration when passing slow pokes. I'm not an expert but I suspect that filter was clogged enough to give a somewhat erratic and less than optimal fuel pressure to the injectors that resulted in a slight imbalance in the cylinder combustion.
I don't know when the filter was ever changed but it was a BMW logo stamped Purolator PFC-39 filter.
Sorry for the out of focus images as the only digital camera I have is in my cell phone and it doesn't do so well on close ups. But you'll get the general idea of how bad the filter was.