Onan Diesel Generator problem

Buy a long piece of hose and drop it into the fuel filler neck and connect to the generator. It has an onboard filter so you should be fine. If that works go to the fuel tank and remove the pickup tube and inspect. Replace hose as needed. Installing rubber hoses onto barbed fittings is a recipe for disaster if not done carefully. I always cut the hoses off versus pulling them off if the connectors are barbed. A torn piece of hose can act as a flapper valve and slow or stop the flow of fuel. In one case a tiny piece was actually cut loose and lodged into one of the carbs on my friends airplane. That was fun to diagnose and repair.