Here is what the K&B site says (bold emphasis is theirs, italics are mine):

AIRBORNE BREAK-IN

1> BREAK-IN running should be done with the recommended propeller at a slightly rich setting. You want the engine to be at running operating temperatures. The needle valve should be set at a point just into this range from a four cycle setting. Fly the plane at maximum throttle for 2 minutes, then throttle back to half throttle for approximately 30 seconds. Repeat this sequence until approximately 20 minutes of accumulated running time has been obtained...