Briggs and Stratton 550 series Craftsman lawn mower, I can not get gas in the carb.?

I changed the prep on and just get air. I bought a can of air to blow out the carb, when I blow into the pipe going into the engine, gas wanted to fill the carb. It starts when I fill the carb with gas than stalls due to not getting gas. Please help with any suggestions All welcome.