The BMW R90S motorcycle was produced from model years 1974 to 1976. The R90S Owners Club is a worldwide organization devoted to this iconic motorcycle.

There is a thriving mailing list/forum. This is by far the best resource for your R90S questions, though this web site is attempting to become the (English language) repository for all things R90S.

The other great resource is the Airhead Boxer Mailing list ("the Airlist"). This is another free mailing list. Visit here to sign up. Once you've joined, in addition to getting daily emails from other airhead owners, you can search the Airlist archives for old discussions of tech issues.

The (U.S.-based) R90S Sport Owners Club ceased operations around 2012. This web site acts as an archive of that club's web presence, as well as a reference for R90S fans and owners.