Don't know if this is any help or not, I got an old 82 Virago that is very close to my heart, that's the reason I could not get rid of her when I got my 1100. The old girl is the same as what you are sayin, I just deal with it and let her warm up good, then all is well. Been that way from the start.
Takes at least as long as you are sayin,to warm up good, if not more, nature of the beast. Hope this helps a little, maybe others have a good answer. Ride Safe.......