Take the air cleaner off and look into the carb. It should squirt fuel when you open the throttle. Otherwise your accelerator pump isn't working. Most old inliners started the best with 2 squirts. Most people of my generation who learned to drive were taught to pump the pedal twice before cranking. If your accelerator pump isn't working, and it is going to be difficult to start. And it is very likely that it isn't if it sat 25years. Back when your chev was young, it was common to pour a couple of table spoons of gas in the carb until we got around to rebuilding the carb.