1992 Chevy K1500 5.7 hard to start

I have a 1992 Chevy K1500 5.7 liter engine that is hard to start. I know the fuel tank has pressure because it releases when I open the gap cap. If I put some gas down the carburetor then it starts right up. A friend talked about a primer under the carburetor could this be it? If so what is this called and how can I diagnose that. Thanks for all your help, Beth.