This link will get you more familiar with the carb. Sounds to me like your carb is flooding from perhaps a crumb of trash on the needle valve seat attached to the float that regulates filling the float bowl up as the engine takes a sip of fuel? This would occur when you do not have a inline filter between the fuel tank and carb.
Or you could also simply have a float out of adjustment. Norm;s pictorial shows this better. http://motorbicycling.com/f39/motori...build-302.html
Think of the carb float assembly as a upside down toilette valve so to speak.