Here's a good primer on Walbro carbs in general
http://www.drystacked.com/Walbro%20Carburetor%20Theory%20ebook1.pdf
Roughly the small carbs have a bottom bowl and top one. The line from the gas tank with the heavy weight attached goes to the top bowl On mine a WT312 it's on the side with the choke. The bottom bowl goes to the input side of the Primer and the output line from the primer returns to the tank vie the third non-weighted line.
Is the Primer pumping the right direction? Fuel should be pulled down the line from the bottom bowl and back into the tank. Watch the bubble to be sure. I think there are 1way valves in the carb so it the fuel doesn't pump easily you might have them veversed.
SMack
April 2008