18 hp fuel help

I have a 18 hp Briggs that has had lots of abuse I picked it off a local in town he planed to scrap it but instead i got it and I have had it running but it won't suck gas it is the style with the fuel pump on the side of the carb and I have changed the carb seals and pump diaphragm with new ones and it was cleaned then I tried it and still nothing but it will run with gas in it and the rank is not plugged and has fresh gas in it help me please