truck turns but doesn't start

i have an 83 chevy c20 with a 5.7 350. i recently bought this truck and it drove just
fine,needed a little tune up but over all ok. the day it broke down i was driving my kids
to school and it sputtered like it was going to run out of fuel but kept going fine after
that. the fuel gauge was stuck on full so i didnt know how much is in it. about a few
hours later i was driving to work and it stalled out,like it did run out of fuel. so i put 5gal
of fuel in it and a little in the carb and it would fire with fuel in the carb,but after that it
would just die and and turn over but not start. so i towed it home and assumed it was
the fuel pump and replaced it. the previous owner told me to not used the selector
switch and couldnt tell me why. so i replaced the selector valve by the tank so i can use
both tanks. the switch in the cab broke when i tried to use it but after replacing the
pump and the valve i still get the same results of it only starting if i put fuel in the carb. i
put 5 more gals of gas in the tank but still nothing. i did notice that when i turn the key
over i hear a loud clicking noise coming off some type of electrical part on the carb. am
i skipping something? sorry this is so long,just want to give full detail of whats going on.