I was wondering what is the lowest possibly oil viscosity I could use for my little ninja, zxr250c. I've recently changed from a 20-50w rating, I think, to a 15-40w. It obviously feels better having fresh oil. I was thinking of maybe a 10 rating but was wondering if that was too thin. Reason being, compared to the older oil I was using, morning start and idle seems so much better. I don't have to have the choke on, reving it at around 4,000rpm at 4am in the morning. It still jumps up and down to 4,000 but after a few seconds I can take the choke off without it stalling. Anyway is there a thinner oil and is it safe to use on my bike?