Most modern "leaded" bikes will run on unleaded just fine. The catalytic converter if they have one will be ruined by the lead, so most people either ignore it or replace it with a piece of pipe - available for BMWs in several places.
check the Which Bike forum for more, and also the last few issues of the ezine have had a discussion on the subject for BMW's in the sidebar. You can also just search the site or HUBB for comments - this isn't a new subject, it's a frequent question.
I am moving this post to the Which Bike forum, as it's more appropriate for it.
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Grant Johnson
Share the Dream!
at:
www.HorizonsUnlimited.com