1973 240z. What is the other line on the fuel rail for, the one not connected to the fuel filter? Is it a feed to the carbs or is it a return?

I want to cap it, im trying to clean up my engine bay but it kinda looks important

It's a return line. According to some of the threads I've read it can be eliminated if you use a fuel pressure regulator. 3 1/2 lbs. seems to be what everyone runs on SUs.

Mark in Portland

  Mark Maras said:

It's a return line. According to some of the threads I've read it can be eliminated if you use a fuel pressure regulator. 3 1/2 lbs. seems to be what everyone runs on SUs.

Mark in Portland

thanks. I flipped through the forums using "eliminating fuel return" and there are mixed opinions about it. I guess I shouldn't eliminate -if unsure, dont fix what's not broke.

Removed return line two years ago, no problems. I have a different fuel rail that doesn't pick up as much heat from the engine as the stock one. Fuel pressure usually stays between 3.4 and 3.9 psi while driving. I have seen pressure drop to about 2.5 psi once on the freeway (parking lot conditions) in hot weather, that might have been a warning of impending vapor lock. Only time it ever vapor locked it was 120F, when I still had the return hooked up.

Thought about using the return line as an extra fuel tank vent (might need to run a line to the air cleaners or under the car to prevent gas smell), or use it as a return for a fuel pressure regulator. For now it's capped.

Yeah. I agree. I'm leaving mine on my 260. I thought about changing it but I'm trying not to get caught up in the " as long as I'm here I should". When I really thought about it, that is so far down my list of to-dos that it may never get done. It's a long list. But for those who truly have Z fever it doesn't matter, It's a labor of love with huge rewards that few understand.

Mark in Portland

  Stanley said:

Removed return line two years ago, no problems. I have a different fuel rail that doesn't pick up as much heat from the engine as the stock one. Fuel pressure usually stays between 3.4 and 3.9 psi while driving. I have seen pressure drop to about 2.5 psi once on the freeway (parking lot conditions) in hot weather, that might have been a warning of impending vapor lock. Only time it ever vapor locked it was 120F, when I still had the return hooked up.

Thought about using the return line as an extra fuel tank vent (might need to run a line to the air cleaners or under the car to prevent gas smell), or use it as a return for a fuel pressure regulator. For now it's capped.

might be a stupid question but what is vapor lock? Are you running stock mechanical fuel pump? Can you show a pic your "different" fuel rail? I was planning to cut the hard lines along the firewall and attach a hose from the firewall to the carbs directly -eliminating the two hard lines on the left side of the engine bay (when looking at it head on).

Just have mechanical fuel pump for now. Removed the electric one at the tank and put a filter there instead. The fuel rail is welded steel tube connected with a short length of fuel hose to a hose barb on the fuel pump.

Right under the glass filter see where I capped the return line. Doesn't look great. The other hose from the mechanical fuel pump goes to a fuel pressure gauge under the glove box.

Seems to me your idea is OK but I'm not the expert.