I use Valvoline Racing Oil. I used to use Castrol, but I think it produces more "ash". I have no idea what I'm doing though, either. Maybe ash is a good thing (?). This is the kind of thing the Bemer guys relly sink their teeth into
. I suspect that any good oil is OK to use. I've heard pros and cons on regular vs synthetic vs car type vs motorcycle specific oils. I know they're different kinds of engines, but EVERONE who knows anything about Indians says to use Valvoline Racing Oil.
For some reason, mixing viscosities yourself is not the same as buying it. 10-30, for example, is basically 10 weight oil with additives that makes it thicken up when it gets hot, but it's not actually 30 weight oil. Single viscosity oil is more "pure", if you will, and will withstand heat and shear better. For some reason, mixing viscosities yourself gunks up the engine. I work with some mechanics who often cluck their tongues when they look under some valve covers because of that.
There has been a fairly regular brouhaha about putting car oil in motorcycles because the theory is that car oils today are too slick and will cause clutch slippage in MCs. Well, if you've been using car oil and it works- keep using it. If your clutch slips, try MC specific oil. My 2 cents.