I have 720 D that has not run in 20 years. The pony starts fine and I can turn over the diesel motor on decompression with no problems. I have emptied the diesel fuel from the tank, and removed the sediment bowl and cleaned it. I removed filter housing and replaced the two fuel filters. I reattached the fuel housing and reconnected all the lines and put new fuel in the tank. I removed the bleed bolts from the filters and opened the sediment valve, and NOTHING. Fuel will not flow. When I disconnect the line between the sediment bowl and the pump, the fuel flows fine. When I connect the line, there is no fuel flow past the pump. How do you bleed out the air if the fuel will not flow into the filters? Should the fuel flow freely through the pump?