The truck has sat for a while. Chances are your gas tank has plenty of rust and varnish in it. If the truck was stored with gas in the tank, that gas went bad a long time ago and turned into varnish. Putting new gas in the tank will dissolve the varnish and move it into the engine where it can cause many more problems with the carb and valves.
Replace the fuel line from the fuel pump to the carbuerator. (you can use a flexible fuel rated rubber hose for a temporary fix) Remove and plug the fuel line that feeds the fuel pump.
You can run a temporary fuel line from a portable gas can to the fuel pump.
Note: Carbuerators do not like to sit for 20 plus years
Note: Carbureators do not like rust or varnish in the tank
Note: The carburetor will need to be taken apart and rebuilt, or replaced with a good carberator.
As stated in earlier threads, A compression test is necessary at this time to determine weather or not the engine will start.
The good news... the engine turns over, you do not have stuck cylinders.
The bad news... the engine has sat for several decades. It may not have ran when parked.
More bad news, trying to start the engine without cleaning the gas tank and lines may have wrecked your carb. If some of that dirty gas got into your engine, the varnish may stick some valves and bend some pushrods
Your engine could start even with a bad carb and fuel pump if you poor a couple teaspoons of gas directly down the throat of the carb.
OK, one more dumb question, when you are trying to start your truck, Do you have the ignition switch on, and does it work? The truck will crank over for a long time without starting if your ignition switch is off.
