OH-NO Twolanerider, you just had to do it--didn't you? You just added another item to my list that no one can agree upon ----- service intervals. (--- 1500 miles -- in my engine that oil has seen half of it's life span already.)
That whole service interval question is indeed incredibly, indelibly, indelicately and sometimes indecisively important; in an indelicate sort of way (since it makes some people go all wonkly [a technical mental health term {I just made up}]). I can not say I follow any published suggestions for my own service methods and intervals (except, of course, that once this post is posted that posting will post and publish so no longer will I be able to say I follow unpublished service intervals because they'll no longer be unpublished due to not being unposted by this unpost; once it is posted [though not Postally {but, instead, digitally}]). But I digress....
Chit, forgot what I was talking about.
Never min...
Oh yeah; fluid changes.
I change my engine oil every 5k miles. Both engines (don't have two in one bike but two bikes with one engine each) need topped off with a half quart at 3500-4000. I often give them that when they need it. Unless they've been bad. Then I sternly tell them they're going around the block without desert and they have to just like it; whether they like it or not!
At 2500 I do drain the oil and run it through the nylon hosiery of virgins before pouring that oil back in the bike. I tried the more parsimonious approach of using the hosiery of unvirgins (1/2 price!!) but the... um.. well... uh.... byproducts, yeah, that covers it, the byproducts worried me. So it's only white nylon hosiery from virgins for my preservice filtration.
At 3500 I also pull the oil caps off each bike overnight and play "The Flight of the Valkyries" all night long in the shop. This is because the music will scare the crap out of many of the combustion byproducts and they'll run away out of the opened oil fill hole. This only works when starting with a warm engine though as some distillates, no matter how frightened, can not escape through a more viscous cold fluid.