???

my truck was setting for a couple of years before i bought it, i had another good used motor put in it and used my original carb on the new motor and my gas tank had a little bit of bad gas in and the guy just added a little bit of good gas to get it home, drove fine on the way home and for a couple of days, now it will not start unless i put gas in the carb and then it only runs a couple seconds, i put a new fuel filter on it

fuel pump?

if the gas had turned or started to turn to varnish, it could have clogged up the fuel lines, filter, or even the jets in the carb......you may have to take
the line loose at the tank, and carb, and use a compressor to blow it out.
if that doesn't fix it, you may have to tear down the carb and rebuild it.

good luck w/ it!