Update:
It turned out to be a problem with the stock fuel line to the clunk. The stock line is small flimsy hose and I discovered that it could possibly double back on itself and wrap around the air vent line inside the tank. I replaced the line with standard fuel tubing which was stiff enough that it shouldn't do that unless I hit something really hard. Now it seems to be running like a champ again with the same fuel and glow plug I started with.