breaking in engines is best done per the manufacturers instructions, I do mine in the plane at the field with the plane tethered. I do this with my large 4 strokes all the way to my smaller 2 strokes that I race with. If the plane has a cowling on it , I leave it off for the first 2 flights or so after i break in the engine for adjusting needles etc.... The biggest concern I see with people breaking in engines is leaning them out to fast, especially on 4 strokes. Get with someone experienced at your field to help...

if you need specific help with an engine dive us the make, size and type .....