The FIRST thing I always do when I get one of these old cars is inspect the fuel tank. If it even looks suspicious, out it comes. I rinse it out and look closely in it to see if there is any rust and scale. If there is, I chunk it and get a new one. If not, I clean hell out of it. 30-40 years of crap buildup in the tank and nobody ever thinks to clean or replace the tank when they buy an old car and the they wonder why it's runnin like hell.
The tank is the source. If the source is not clean, you will continually have problems. You need to remove and inspect the tank. Until you do that, you're just chasing your tail.
