I just replaced my pilot jet. When I took out the one in the bike it was a 65S. I went to go buy a new one and they didn't have any 65S's just 65's. I asked their mechanic and another mechanic at another shop and they said there was no difference. When looking at them though it looks as though the 65S had slightly smaller holes (you could see this w/ your bare eyes). Maybe it was corrosion from being a old jet but I'm not sure. Does anyone know anything about this?