Dumb question

[M491Cabriolet]

Hi all. I am trying to not make any mistakes. I’ve redone almost all my fuel lines on a 1974 911. Which of the circled lines is the feed line, and which is the return? I’ve been searching a lot, but can’t seem to find the definitive answer. I hope this will be a no brainer... Thanks.

[boyt911sc]

The fuel delivery line from the FP is connected to the fuel accumulator. This is the correct set up. However, if you inadvertently interchanged the connections, the best way to definitely identify the delivery fuel line is to test run the FP for a second or less. And you will find out which one of the two (2) hoses have fuel delivery.

Another method is to connect a fuel pressure gauge to WUR/FD and measure the control and system fuel pressures. The correct set up will give you control and system fuel pressure readings. Wrong connection will give you a very high system pressure reading.

Tony

[M491Cabriolet]

Thanks. So, the fuel line that is on the left, coming through the frame is the one that is normally the feed line, and the one that comes through the rubber seal at a lower point is normally the return? Thanks.

[boyt911sc]

Originally Posted by M491Cabriolet

Thanks. So, the fuel line that is on the left, coming through the frame is the one that is normally the feed line, and the one that comes through the rubber seal at a lower point is normally the return? Thanks.

I have personally seen and tested an engine that the owner inadvertently switched the fuel lines. The standard fuel lines for the delivery and return have the same size metric fitting. So for someone NOT familiar with CIS could easily make this blunder.

So to positively identify the fuel delivery line is to test the FP and confirm which line has the fuel flowing out. All you need is a very short run of the FP to confirm it.

Tony

[M491Cabriolet]

Thanks, Tony. Agreed and will do, but from the factory, which was feed and which was return?

[frosty2]

On my 73 I have carbs not cis and no return line just the supply and it is the one circled on the left coming out of the frame if that helps.

[M491Cabriolet]

Thank you, it does! I appreciate it. Thanks.

[boyt911sc]

Originally Posted by M491Cabriolet

Thanks, Tony. Agreed and will do, but from the factory, which was feed and which was return?

If you have the OEM fuel line for CIS it will have the bend tube connector to the fuel accumulator. So it would be easy to identify the delivery fuel line.

Tony

[manbridge 74]

On my 74 the furthest left side is pressure line from pump.