I changed my oil recently and thought I had it at exactly the upper limit. I rode the bike a couple of times and really noticed it seemed slower to rev, and not quite as fast. I double-checked the oil level and I'd actually overfilled it, and not by much; maybe a half-cup, which I drained out. That put the oil level about 3mm below the upper line. The engine ran perfectly after I corrected the oil level.
The extra oil actually does begin to rob power as the crank has to slog through it. Best to keep the level a few mm below the upper limit. One guy blew out a valve cover gasket from over-filling his FZ8, there is not a lot of room for error there.
I have just under 10K miles and finally switched to a semi-synthetic which certainly did improve the shifting, especially from 1st to 2nd.
The extra oil actually does begin to rob power as the crank has to slog through it. Best to keep the level a few mm below the upper limit. One guy blew out a valve cover gasket from over-filling his FZ8, there is not a lot of room for error there.
I have just under 10K miles and finally switched to a semi-synthetic which certainly did improve the shifting, especially from 1st to 2nd.