Alright, I inherited

(honestly) a Robin fl500 backpack blower without manuals. It was great to use :cheesygri (much better than the homelite blower mulcher) until I ran out of fuel. Problem is I don't know the mixture and afraid to use 50:1 like my homeowner stuff. I tried the web, but couldn't find manuals. I emailed the regional Robin rep, but never heard back. Then again, 99% of these things "inherited" are probably "hot."
I'd like to use it again soon, anyone got one?
Thanks.
Neil