Why does my gas boil and and full tank disappear quick

Fuel lines too close to a heat source is the most common problem. I have used heat wrap tape to help vehicles that do this, but sometimes it is just not enough and wind up making up fuel lines to reroute them. As this is a much older vehicle I would start looking as to why there is so much heat, like catalytic converter problems, air fuel mixture wrong due to O2 sensors, vacuum leaks and so on.

This is called vapor lock. It's pretty much unheard of anymore. Two other things to check are the exhaust manifold heat riser, if equipped, and the thermostat controlled air cleaner assembly. If the heat riser is stuck closed hot exhaust gasses will be constantly directed to the intake manifold, under the carburetor, and cause the carburetor to overheat and the gasoline to boil in the float bowl. The same is true if the thermostat controlled air cleaner assembly is not working properly. In the snorkel of the air cleaner assembly is a damper door. When the engine is cold the damper will be closed allowing only preheated air to enter the air cleaner assembly from the small metal hose that's on the bottom of the snorkel and attaches to the heat stove on the exhaust manifold, usually on the driver's side on a GM. If this damper is stuck closed hot air will be constantly pulled into the air cleaner assembly and, again, overheat the carburetor. As the engine begins to warm up the damper should open. In cold weather the damper will open and close as needed to maintain a temperature of about 100°F inside of the air cleaner assembly. Hope that helps! Jim