I use Echo weedeater/chainsaw oil to break in a new engine as it is petroleum based and seems to be a good quality product. It is available at many power garden/ranch products dealers. As the other guys stated, most of the 2 stroke synthetic motorcycle oils are very good after break-in. You don't have to be in too big of a hurry to switch to synthetic oils as many engines need a pretty fair number of hours to get properly broken in with the non-synthetic stuff. The Zenoah's, for instance, really need a pretty long break-in period it seems.

Sam