If the main bearing is "rumbling" then its no good. Once its all washed out try lubing it with some very light oil and feeling it again. They always feel alittle rough if they are second hand and washed out. With 2 stroke mix washed into them they should feel perfectly smooth.

You can also try pulling the outer race side to side. A new bearing has almost no sideways movement.
_________________
If I have to take the carbs off once more...