Ok, so at one point the "carburetor rotor" was getting hung up on the "mixture control valve assembly" and was not able to close all the way. Unscrewing and rescrewing the low needle helped and now it has full range of motion.

Today I got to the field and my old instructor was there, and he said a guy was coming who knew all about engines. He helped me tune her up, which included richening the high needle and leaning the low needle; it was sounding pretty good, blowing plenty of smoke (it's still new) and idling great at 2100rpm and topping out at 12000rpm. I had 2 good flights on it and it deadsticked on my 3rd takeoff. My first dead stick! I kept the wings level and put it down as gently as I could - it landed in a giant puddle and somehow missed the corn, so no real damage.

We cleaned it up and started it up before leaving, and it started up, advanced fine, got to full rpm and cut out. Tried it again and the same thing happened, so now my engine is cutting out at full throttle, though sounds just fine getting to that point.