If you read and follow the instructions that came with the engine you will have an engine that will last many years and give you good service. The reason we use tacho's on 4strokers is to set the RPM so they won't over rev in flight. After break in go to full throtal and slowly(SLOWLY) lean out while watching the tacho(DO NOT GO OVER MAX STATED RPM). When rpm stops to increase richen up a couple of clicks and it will be set.

Cheers