12" Milwaukee. Why does it lose power after it has been run for awhile?

Hi,

Assuming there isn't some other mechanical problem or the saw isn't being overloaded, most circular saws have motor brushes that can wear out after extended use. These brushes are usually replaceable. When the brushes are worn, they will not deliver sufficient power from the motor stator to the armature (the part that rotates).

Here is a link to a parts supplier. Find your model number and look for brushes.

http://www.ereplacementparts.com/milwaukee-circular-saw-parts-c-131_5128.html