just a shot in the dark here: one of your springs is worn out, causing the system to be imbalanced, resulting in full auto fire and the sear not catching.
Replace the springs with appropriate length new ones.
Sear/bolt surfaces are worn and not catching: examine the surfaces for wear.
Disassemble and recheck all parts while looking at gun diagram to be absolutely positive you have every part and it is in the right place (I hear bumpers often end up in the wrong spot.)
edit: after writing that last bit, I think you might have the bumper in the wrong spot.
__________________ "Certainly there is no hunting like the hunting of man and those who have hunted armed men long enough and liked it, never really care for anything else thereafter." Ernest Hemingway, "On the Blue Water," Esquire, April 1936
In the world I see - you are stalking elk through the damp canyon forests around the ruins of Rockefeller Center. You'll wear leather clothes that will last you the rest of your life. You'll climb the wrist-thick kudzu vines that wrap the Sears Tower. And when you look down, you'll see tiny figures pounding corn, laying strips of venison on the empty car pool lane of some abandoned superhighway.
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