FUEL LINE BYPASS

[rebar1111]

Is the mechanical fuel pump on a 2l internally protected from overpressure or does it depend on the external lines that return fuel to the tank?

[bradartigue]

The pump is what generates the pressure to begin with, so it isn't regulated in so much as it is the regulator. In a stock configuration excess fuel is returned by the carburetor via a return line.

[MrJD]

I have heard lots of people remove the I have heard lots of people remove thefuel return line. How does that work? I thought the return was a necessity.

[vandor]

Very early Spiders had no fuel return line. It was later added to reduce vapor lock.

[bradartigue]

I have heard lots of people remove the I have heard lots of people remove thefuel return line. How does that work? I thought the return was a necessity.

It isn't necessary, and as Csaba noted it was only added to reduce vapor lock, and only on USA cars. Very little fuel actually gets recirculated (the return feed is a 1mm orifice). If you want to delete it you can, but if it is there go ahead and use it. If you want to create a return loop and your carburetor does not have the return pipe then use a fuel filter with a regulated return, about $5.99 at Auto Zone. These look like a normal metal barrel filter but have a third, smaller pipe for the return.

[rebar1111]

Thanks for the response. My intent was to install a 2PSI regulator ahead of the front carb of a twin IDF installation but was concerned 1) in too little pressure (with the external bypass to the tank) and 2) rupturing the mechanical fuel pump diaphragm ( if I plug the bypass).

I have interpreted the responses to mean that it is OK to plug the external return to the tank and that that action would not cause failure of the mechanical pump.

[fiat218]

I thought it had to be 3 psi

[bradartigue]

Thanks for the response. My intent was to install a 2PSI regulator ahead of the front carb of a twin IDF installation but was concerned 1) in too little pressure (with the external bypass to the tank) and 2) rupturing the mechanical fuel pump diaphragm ( if I plug the bypass).

I have interpreted the responses to mean that it is OK to plug the external return to the tank and that that action would not cause failure of the mechanical pump.

Nah. The fuel pump isn't affected by the presence or lack of a return line. Not enough pressure being generated to matter and keep in mind there is always a constant flow, however small, so long as the car is running.