Tight valves or the fuel pump pushrod siezing up in the plastic block are the 2 best suspects, a squirt of gas down the carb or a temporary outboard motor fuel tank gravity fed directly to the carb will answer the fuel pump question. Setting the valves extra loose and clattery would answer the valve possibility, but if that's the issue why is it getting so hot?, wrong shroud, wrong fan?, chrome parts on the engine?, hmmmm....?