Fuel blockage on seafari

[McGillicuddy]

I think I have something blocking my fuel flow causing my fuel pump to work harder than it can.

I ran about 50 miles last Sunday and ran flawlessly, but when I got back to the kelp beds I put it in idle and we started drifting to fish. After about a minute of idling, the motor would die.

I know the pump creates about twice as much suction at speed than at idle so to some degree that substantiates the ability to run at speed. Switched over to auxiliary tank to run home and idle was fine - in fact I let it idle for 15 minutes at the dock while fetching the trailer.

I've removed the horizontal brass fitting and it doesn't seem to have a check valve. Wondering about the supply elbow on main tank. If I unscrew that what will I find? Is there an anti-siphon valve within that elbow? Or is there crap in the pickup tube? How would I determine that?