1995 Chevy S-10 95 S-10 Blazer wont start

My blazer will not start unless you spray starting fluid of place gas into intake then it starts fine and runs fine after it starts if it runs for a while(15-20 min) you turn it if and start it again it usually starts right back up. Seems like not enough pressur to start from cold how do I check for pressure and what can I do to fix this problem thanks in advance for your help!