The correct run in procedure for a merc/mariner outboard is as follows:
Use double for the first tank full.
Avoid long periods of idle and full throttle for the first 10hrs.
Constantly vary the engine speed using anything up to 3/4 throttle. Avoid long periods at the same speed.
After the first 10hrs use short periods of full throttle (2-5mins every 15mins).
After 20hrs or 3 months return engine to dealer for its 1st service.