Breaking a motor in on the rich side will not damage a motor. Extra lubrication will cause lower temps resulting in a less than perfect fit between the cylinder and piston in the end of the break in process. This means you will have a motor with a little less power but not a damged motor. Breaking it in on the lean side will damage the motor and shorten it's useful life. This little motors are not much different than there 2 stroke big brothers which all require extra lubricatin during there break in. All you trying to do during break in is to get the motor to it's normal running temp. without a excessive load on it and making sure it's getting good lubrication.