Dry Fuel Filter

[TeamBrian]

Whilst my 1600 (Bocar carb and pump) is running, the fuel filter appears to run dry but the engine still manages to run. On closer inspection, a small amount of fuel passes through the filter, and when the engine is turned off, the filter refills. Am I right to suspect a blockage in the tank? I've already changed the filter in the tank due to intermittent running problems. Any ideas?