Gas Leak in 1994 Isuzu Pickup

I seem to have a big gas leak in the engine. When I start the truck, the gas just runs out onto the pavement. It is directly under the engine and not at the back by the gas tank. At first, it only did this every once in a while. But now it spews the gas every time I start the truck! I can't seem to figure out what is causing this! Just tuned it up, put in a new alternator as well as a new battery! And now this! Any ideas what might be causing the leak or how I can fix it?