From the factory there was a filter on the supply side. The line going from the fuel pump to the carb was one solid piece of steel tubing threaded on both ends. It is smarter to keep the filter on the supply side so that you can use a solid piece of tubing from the pressure side to the carb. This minimizes the potential for a fuel leak on the top of the engine from either the fuel filter or the inevitable rubber hoses that attach to it. The way the factory did it meant that most old rubber related fuel leaks would be under the engine, less threat of a fire there.