Cleaning fuel line

I've had problems with lack of fuel to a single carb type 3 motor. Its been off the road a few years, tank was removed and water blasted clean. Line was blown through, new fuel hoses, fuel filter etc.

Had been running the car a week with no problems. I put some of that fuel system cleaner, thinking more about the carby as it hadn't been stripped down.

Now have problems with low fuel. carby kit turned up (32PHN carb) and installed. Fuel floats appear sound, not leaking.

I am going to run it out of a fuel tin (just idling), but it looks like the metal fuel line has a loose piece of crud which flaps around and shuts the fuel off. Is this credible, anyone else had something like this happen?

The line has already been blown through, is there another way of cleaning it out?

Any help appreciated, very frustrating problem.