If the engine is ringed and hasn't been broken-in completely, be prepared for a long and tedious break-in trial. The websites mentioned should get you started on the break-in procedure. Follow it and don't take short cuts. Peaking out a ringed engine too soon can result in losing the tension in the ring's metal and require replacement. Not all that difficult to do, but then you are back to square one in the break-in process.

Ed Cregger