Over the past two years, my TN75DA tractor had become increasingly hard to start and sometimes required "Quick Start" (ether) to get it going. I changed the fuel filter but this did not resolve the issue. I then drained the fuel tank and found that the contained diesel looked more like dirty dishpan water. I added 1/2 tank fresh diesel and the engine appeared to start easier. However, the hard starting condition reappeared. The tractor would start fine one day and then wouldn't the next. Also, the tractor would be running fine, but, then would not restart after being turned off for an hour. It was obvious that the engine was starving for fuel so I turned my attention to the fuel pump. The pump runs solely by mechanical action via a fuel pump cam shaft which is (internal) in the engine. The fuel pump was easy to remove: 2 nuts at the flange location and 2 banjo bolts (one on the suction side and one on the discharge side of the pump). Note that the banjo bolts themselves need to be inspected for entrainment of solids (which needs to be removed before reinstallation) as well as the cavities on the metal hose ends that the banjo bolts pass though when bolted back to the pump. When I disassembled the fuel pump, I determined that the hard starting issue was indeed due to it malfunctioning. The pump contains two small rubber check valves, one on the suction side and the other on the discharge side, I found that both of them had broken off from the ports that they were designed to be attached to. How does the pump function? Here is how I see it (hopefully I am correct): the check valves cycle open and close probably hundreds of time per minute when the tractor is running. When the pump drive cam lobe connects with the fuel pump lift arm, a spring in the fuel pump that is attached to the pump diaphragms is compressed and the pump's diaphragm actuates downwards - creating a suction - the fuel is thus sucked from the tank into the fuel pump. As the cam lobe rotates away from the fuel pump lift arm, the fuel pump spring, which is attached to the diaphragm takes over, forces the diaphragm upwards, and ejects the (now pressurized) fuel from the pump. The fuel now travels to the fuel filter. With the check valves detached from their locations in the fuel pump, the pump cannot adequately create the suction & pressure cycles needed to pump the fuel from the tank and onwards to the filter - the pump in essence is likely just causing the fuel to quiver back and forth. The fact that my tractor did start normally on occassion was probably due to the check valves being close to their design locations by fluke (than anything else) and still being able to fulfill their design roles. Although the check valve stems broke off and rendered the pump useless, the pump likely was in service for 10 years and did serve its function well. The total cost to replace the pump was an hour of my time and $80 for a new pump, one gasket, and 4 banjo bolt washers. I searched the internet for a video that explained/detailed this but came up empty handed so I thought I would contribute and create one. I hope it is of use to you!