69 340 problems

To rule out the fuel problem, put a fuel pressure guage on a tee to the carb line. That way you can monitor the fuel pressure while engine is cranking and running. I had the same problem with a 340 a while back, it took the press guage to verify a plugged fuel line and suction sock. When I blew air back thru the line, it started up again but plugged up quickly. The tank was full of rust and the suction sock was clogged.