D special fuel pressure
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  1. #1
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    May 2014
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    Default D special fuel pressure

    Hope to tap into the collective wisdom...

    My 1970 d special is equipped with a non standard electric fuel pump. To supply the carburettor.

    I wanted to investigate the pressure this pump produces and the fuel circuit. The reason for this is the electric pump runs constantly with the ignition on, in my experience this is not normal.

    Can anyone advise:
    1. The standard mechanical fuel pump pressure.
    2. If the standard system has a return to tank - or if anyone can explain or point me to a reference for the circuit diagram.

    Thanks in advance
    Alex

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  2. #2
    Fellow Frogger! citroenthusiast's Avatar
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    Apr 2014
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    Phoenix, Arizona USA
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    Default

    For carburetors, fuel pressure is 2-4 psi.
    There is no return. The fuel line dead heads at the carburetor.
    Older style fuel pumps (e.g. SU electric pumps) have a demand switch that cycles the pump when fuel is needed, so you can hear them stop after the float bowl is filled, before you start the engine. Many newer style pumps (e.g. Facet) seem to run continuously, but it you listen closely you can hear the pitch change after the float bowl is filled.

    For EFI, everything is different. The fuel pressure is higher and there is a fuel return to the tank.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

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