Darn Chris, Makes me want to build a single seat Bensen with a Mac. It was so much fun!I only used the "original" mechanical pump until it failed, twice.!!! I remember coming in at least twice pumping away on the fuel tank manual pump to keep my engine running. That was maybe 1971. I switched over to the marine pulse pumps and used a tapped hole on the magneto end of the case for the pulse. I also found the attached directions for plugging that original hole in the Mac, straignt from Bensen's manual, 91-H page -4-. I used the pulse pump on my Bensens and the Parson's tandem and never had pressure problems after that.