Hello, welcome to JustAnswer. because of the range of possible issues, this may take more than one post. Please, don't hesitate to reply.
Fire up the motor and bring the rpms up to about 1000 then cover the bottom carb with your hand completely.
Tell me if it gets wet with fuel when you do that. (the motor may start running better when restarted after doing this)
You are only using one carb.
Pull the bottom carb and find out why no fuel is getting thru it, Chances are the needle valve is just stuck so no gas can even get in. This should fix your run problem