A client’s car seams to be starving for fuel. It has the 2 port mechanical pump as well as an inline electric pump as back up. The electric pump is mounted along the rocker under the driver’s seat and uses a one way valve in the factory line so either pump can be used. There is a “T” plumbed in line between the mechanical pump and the metal OE style filter. This “T” is connected to the smaller (return) line to the tank. After use of the electric pump last week to overcome vapor lock, the mechanical pump is unable to maintain pressure. I have measured .5 to 1.0 psi at the carburetor until I block the return and then get 4.5 psi from the mechanical pump. The electric will still generate 4.5 to 5.0 even without blocking the return. Should there be any type of regulator to control flow through the “T” back to the tank on a 2 port system? If not, I assume the mechanical pump is weak or producing low volume?
Greetings Eric –
The original fuel supply from the factory only used the mechanical pump and this worked well if the whole system was maintained in good shape. The added electric pump was possibly added to compensate for other parts that had begun to fail. If it in fact worked well with these changes for a while and the filter is not plugged and the hoses and lines are intact, some other weak component could now have deteriorated further. The mechanical fuel pump is a strong possibility as you suggest and is a common failure item.
Before replacing the mechanical fuel pump another strong area of concern is the fuel sending unit in the tank. You should remove and inspect it as It has a strainer that could be plugged up with fuel tank debris and / or the pick-up tube could be corroded or bent etc. At the same time the vent for the tank should be working properly to vent the tank as fuel is drawn out.
Let us know what you find as we do have the correct replacement parts if any are needed.