1988 s 10 2.5 I start the engine in the morning or

1988 s 10 2.5 I start the engine in the morning or after 3 to 4 hours of sitting. It idles fine and runs great for about 30 seconds to 1 minute. Then the fuel injector sprays out more like dumps out alot of gas into the carb. the engine finally shuts off and it continues to dump gas into it until im assuming the fuel pump shuts off. After i crank on it for a while it finally starts up and then acts like there is no problem. You could run the truck all day long no problems until you let it set for more than 3 to 4 hours. Any answers?!