Hello Garry,
The fuel system on the W113 cars is a continuous loop. So any fuel pump used must deliver a larger volume of fuel than needed for most cars. The return line to the fuel tank on these cars is like a huge fuel leak. (back to the tank). While all this fuel is returning to the tank, the fuel pump must maintaine around 11 to 15 psi. fuelpressure to the engine. This is not high pressure, but is high volume. If you change to anything else you will need to check the pressure in the system and reduce it if it is too high. If your volume is not high enough the fuel pressure will fall below the minimum during high fuel usage conditions and the engine will miss and buck.
The easiest retrofit is using the later Mercedes EFI electric fuel pump. It was used on the early 450SLs with EFI injection. These are smaller simpler, deliver correct volume and pressure. An aftermarket identical reproduction is made in Japan for less than $200.00 new. As with the original, these are gravity feed and must be mounted near level with the bottom of the fuel tank.
Some high volume racing pumps will work, some won't. Some of these are expensive also.
Joe Alexander
Blacklick, Ohio
