Pump It Up – Installing a modern electric fuel pump to improve a carbureted 1960s sedan

Article and image Richard Simonds

Because of the alcohol content in modern fuels, owners with older cars that have carburetors will discover that the fuel has evaporated from the carburetor after only a few days of the car sitting idle; the mechanical fuel pump will take some time to get fuel from the tank to the carburetors. Running the starter for longer than 30 seconds or so is not good for vintage starters and is not good for engines when the crankshaft, camshaft, pistons and other moving parts are rotating without full lubrication. Mercedes-Benz engines from the early- to mid-1950s had a wire bale that could manually be pulled to actuate the fuel-pump diaphragm to get fuel from the tank to the carburetor(s) without using the starter.

Time for a fix

However, being forced to reach down alongside the greasy engine was not a pleasant task – especially when dressed for an occasion. By the 1960s, those little wire bales had disappeared from beneath fuel pumps. Besides, the prevailing expectation at the time was that these cars would be driven every day; having no fuel in carburetors was not even a consideration for the engineers in Stuttgart. Now that those automobiles have become collectibles, most of them are not driven regularly. Combine infrequent use with highly volatile fuels that are not a good match for the old carburetors to be found in machines of this era, and something has to change.

What to do?

My answer to this dilemma with my own 1969 280S with its dual carburetors was to have an electric fuel pump and pressure regulator installed. The electric fuel pump is activated when the ignition key is turned on; within 10 seconds, the carburetors have fuel. The car starts with a few cranks of the starter. The pressure regulator meets Mercedes-Benz requirements that fuel pumps provide a high volume of fuel to the carburetors at no more than 4 psi pressure. As a side benefit, I have discovered that the engine is smoother at highway speeds because both carburetors are getting equal amounts of fuel. Apparently, that back carburetor was being fed less fuel than the front one and the engine had a high-speed harmonic vibration. It is smooth now.

How to do it

The approach my mechanic took was to use the existing fuel line and hoses from the fuel tank to the mechanical fuel pump, but to disconnect the line to the mechanical pump and feed the electrical fuel pump directly from the tank. From the fuel pump, there is a short hose to the pressure regulator. From there, a new fuel hose goes directly to the carburetors. This completely bypasses the mechanical fuel pump but leaves everything in place if we decide to return the upgrades to original specs.

The new electric fuel pump and adjustable pressure regulator were purchased from Redline Fuel Management, www.redlineweber.com. The fuel pump part is No. 99009.131; the adjustable pressure regulator part is No. 31800.063. The process is quite straightforward, but I recommend having the job done by a mechanic experienced with these cars to ensure that installation is done correctly and the fuel pressure is set properly.

Using highly evaporative modern gasoline in a seldom-used vintage car equipped with a carburetor leads to excessive starter motor cranking before fuel reaches the carburetor, straining old mechanical components. Installing an electric fuel pump and pressure regulator resolves the issue.