Debris more likely, a clogged filter, or air in the lines. Firing on 1 cylinder, or less than 4 is usually air in the lines. A slowing engine is usually starving of
fuel. In the tank, the pickup can slowly clog, but when the engine stops and the
pump is no longer sucking fuel, the vacuum drops and releases the debris. Or the
fuel filter is clogged. If you have a primary with a bowl you would see the water if any. There are cheaper filters with a bowl. Bigger boats use dual filters so a new one is ready to go.
If you add a vacuum gauge between the primary filter and the
lift pump, you can see as your filter gradually clogs. Mine starts at zero and gradually climbs. With experience I can tell how soon I need to change filters.
If you don't want surprise fuel problems you should add a
diesel stabilizer/biocide every fueling and use a
Racor type primary filter. In 60 years on the water, I've never had a fuel problem. But fixed fuel problems for many others.