This site is pretty useful for info on Waldbro carb's. See if any of the problems they list fits yours.

http://tech.flygsw.org/walbro_tuneup.htm

Also not sure if you want to do this but maybe you can flip it over and start it to see if it runs the same on the ground inverted (with the help of a few friends). This would eliminate any pressure problems. BTW, I did notice that you plumbed your vent to the inside of the fuse.