Mysterious brake parts?

Ok so I bought a new master cylinder made by Magura, because I figured why bother with the old stuff when I can put new on. Manufacturer lists the 1980 KZ1000 as a proper fitment.

Still not getting any pressure to speak of. The lever action gets spongy and has a little resistance to it, but never firms up completely. I've checked everything in the system and don't see any leaks. Any ideas?

When bleeding your brakes ,are you pulling the handle back & forth till you get pressure & then opening up the bleed valve ?
If you are, that's your problem, by doing that you're swishing the brake fluid back & forth in the brake line creating air bubbles & you will not be able to get the air bubbles out that way
Just pull the handle in with the bleeder closed once, hold the handle in & open the bleeder, with hose submerged into a cup or can of new or used brake fluid, close the bleeder before you let go of the handle, & repeat this process until you see no more air bubbles & the pressure is built up
It's important to NOT let the resevoiar get too low or you can introduce more air in the system
It's best done with 2 people, one pulling in the handle & replenishing with fluid when it gets 1/2 way down, & one person operating the bleeder valve, & saying when they've opened or closed it
& the person operating the handle should have a soapy rag on hand to wipe up any brake fluid that spills out .....it will destroy any paint on bike or master cylinder
Pete

Thank you for your help. I appreciate your giving time to something so simple.

I have replaced the master cylinder with a new one, and using a vice grip on the brake lines I was able to isolate the problem to my calipers.

Removed calipers and took them apart again...there was trash inside. I had flushed out my lines previously so I can only assume that the flushing shook up some crud which stayed in the lines, and when I tried to bleed the brakes that trash was pushed down the line, where the calipers acted as a filter.

Cleaned the calipers again and now trying to bleed again using your suggested method. Still no pressure.

I'm beginning to get very frustrated. Can't figure out what is going on and it's driving me nuts. This is the last step before I can take it on the road and beginning fine tuning my carbs. Winter is approaching...

It might be those 35 yr. old rubber brake lines deteriorating on the inside, you might want to replace the 3 brake lines with stainless steel braided ones, like many people have done, including myself, they not only look better, but you get more pressure from them
Pete