I am defeated!

[mike_of_bbg]

See the pic below. The relief port is obscured by the reservoir on these round-reservoir master cylinders. It's the port with the red arrow pointing to it. That's actually not just a hole, there's a passage underneath so even when it's clean you can't see into the bore. These ports are notorious for becoming blocked and causing just the symptom you describe. You must remove the reservoir to clean that passage.

[LarryC]

Ahhhh ok I wasn't aware. When I rebuilt my MC I couldn't get the reservoir off. Seeing the hole there and it being clear I decided not to apply the force it would take to remove for no reason.

[Big T]

Ahhhh ok I wasn't aware. When I rebuilt my MC I couldn't get the reservoir off. Seeing the hole there and it being clear I decided not to apply the force it would take to remove for no reason.

You should be able to clear the port with the reservoir on

[LarryC]

Ok well......now that I know its there I will look more diligently.

[Big T]

Take off the MC reservoir cover and slowly (i mean slowly) squeeze and release the brake lever

You should see a spurt of fluid from the return port. It should come up a bit higher than the level of the fluid (a mini geyser)

No spurt, clogged port