If you have plumbed it properly fuel should be drawn through the carb into the primer bulb then returned to the fuel tank.
To check the carb, pull it off the engine then blow air through it.
High volume , low pressure like from a hair dryer that has a no heat setting works best .
If the carb is working you should see the fuel blowing out the other end.
Usual precautions as the stream of fuel droplets in air will go woof with the slightest ignition source.
