Even a small leak in the fuel line will prevent the mechanical fuel pump from working. If the fuel is pulled up, higher than the fuel tank, you can't have any leaks, so make sure everything is connected properly. Next, if the fuel tank has debris, sugar or anything else in it, it could be plugged. Make sure you can get fuel to the filter. You may need to remove the filter, then put LOW PRESSURE air into the tank. It shouldn't take more than 1/4 PSi to push it through. If it won't come through, the tank is probably plugged and you'll need to clean it. Last, if the pump wasn't installed properly, it won't work. Some require push rods to make them function properly, others don't. Make sure you have followed the directions properly for your vehicle. First off, you need to be sure that the fuel pump is not pumping fuel. Disconnect the fuel line from the carb, and turn the engine over a few times. Fuel should shoot out several feet from fuel line. If it does not, it probably means that there is an air leak in the line. A connector is probably loose, possibly at the fuel filter. Also, insure that the fuel filter is connected properly, as reversing the connections may prevent fuel flow.