my truck ran flawlessly for 25 years, then all of a sudden one day gas just started pouring out the carburetor, I checked the float levels and needle valve, it worked fine one day, then it wouldn't work fine the next, I put another carburetor on it it did the same thing, , redid the original carb, but this time I actually took measurements of the float position in relation to the bowl, it was sticking to the bottom when the gas dried out (the first one I still can't figure out.) Then it just ran very poorly, so I replaced plugs wires, rotor, coil, everything. I ran brand new fuel line all the way from the tank to the carb with 2 filters, I tried pertronix, I even tried one of my brand new webers, nothing worked, then one day it just started purring, I have not a clue....
