Hey all. I've found this site super helpful for working on my 1990 K75S and hopefully might be able to help someone in the future here.
A few weeks ago my oil pressure light started coming on. Initially it was just when decelerating from high speed. The Haynes manual suggested that this was symptomatic of a failing oil pump. I gave the bike a look over and found a slight leak coming from the oil pressure sender. So I fitted a new one and problem sorted. The old one was in a pretty bad way, the pin was bent, no wonder it was failing. So, lesson one: if a light comes on it could well be down whatever sensor is responsible for that light.
Changing the oil pressure sender means doing an oil change (and might as well do the filter, even if it only had 2000 miles on it). I spent long time reading around for what oil was good. I eventually took the "these bikes are unstressed and will run on anything of the right grade" advice. So went to Halfords (in the UK, big chain auto parts store) and picked up a bottle of own-brand, semi-synthetic 15W-40. All seems to be fine after getting the bike running again. However, within a couple of days the bike developed the sprag clutch issue, where the starter spins but doesn't engage. Would only happen on a cold start, and not even every time, but still not desirable. I did some more reading around and got the idea that it could be down to the oil, especially since that was the last thing I'd done to the bike. So I went and shelled out for a bottle of Mobil 1 15W-50, fully synthetic "motorsports" oil. Whatever additives are in that stuff seem to have done the trick. It might just be suggestibility but the bike even feels like it runs smoother. So, lesson two: the kind of oil you put in your bike can make an immediate difference.
