On the carb, remove the cover that is retained with one screw. Check to be sure the intake screen is clean. Remove the cover with 4 screws, peel the diaphram back, and push down on the lever at the center of the chamber, to make sure the needle valve is not "stuck" in the seat.
Also be sure the line from the tank to the carb is clear. make sure if the carb has been removed, the impulse holes are lined up in the spacer.
Here is a link to trouble shooting chart that may help:
http://www.wind-drifter.com/technical/walbro_chart.jpg
And here is some info on the WB carb that works like all the others:
http://www.wind-drifter.com/technical/WBManual.pdf