I am restoring a 280z and have decided to abandon the fuel injection.  I know the pros and cons of this or at least most of them.  There are reasons I made the choice regarding mods to the powerplant and my doubts about constructing a custom fuel injection system and programming to match so I don't want to open that debate right now (don't get me wrong I do appreciate whatever advice I get).

 

I had to run new fuel lines because the old ones were badly corroded.  I am using a high pressure fuel pump (because I may want to go back to FI later) and using an Aeromotive regulator to reduce pressure.  So I intend to go out to the regulator and back to the tank with the carbs taking what they need.  

 

My question is about fuel line size.  There are three lines.  Two 5/16" and one 3/16".  I know one 5/16" is the supply.  Should the return be 3/16 with 5/16 to the vent or 5/16 for the return and 3/16 to the vent?  

 

If anyone has a similar setup and would like to share notes and/or a schematic I would really appreciate it.

 

Thanks!

Aw, come one guys.  

FWIW (as Carl tends to say) - the plumbing on my '71 has a 5/16" supply, a 3/16" return, and a 5/16" vent near the coil.  The return is connected to the fuel rail so I don't quite understand your comment on "go out to the regulator and back to the tank with the carbs taking what they need".  Is this info you were looking for?

The 3/16 is the tank vent. Just take a look back at the tank where the hard lines turn into rubber going to the tank and vent. Should be self evident.

The 3/16 is the tank vent. Just take a look back at the tank where the hard lines turn into rubber going to the tank and vent. Should be self evident.

Perfect.  This is what I was looking for!  Thanks guys.  

From what I read at Mallory site and some hot rod chat sites, the return line should be same as the supply line for their regulators. I'd guess they're talking about setups for big dual 4-barrel guzzlers, but it might still apply.

On my '73 at least, the return line is smaller than the 5/16" supply hose barb at the tank (and the vent line comes out of the evap tank). You might want to hook up a fuel pressure gauge to check; on the other hand, if there's way too much pressure the bowls will probably overflow so you'd know anyway. Maybe the other 5/16 outlet would work as a return, but you'd still need a vent.

BTW, the vent line on mine didn't work (per the test in FSM) until I took it out and blasted it with carb cleaner.

  Take care to plan the FPR and related plumbing:

 

Stock 240z's have an orifice at the outlet of the fuel rail to help maintain fuel pressure in the rail. This then feeds the return line which is much bigger than the orifice. So the orifice and the pressure release valves in the mechanical fuel pump work as a team. 

 

In non-stock set ups, simply dead heading (no return used) is one of many designs used  but remember that  fuel flow through the rail takes away heat (and tames vapour lock) so there are advantages to high flow designs too.

If you are getting rid of the fuel injection I would be interested in the BCDD if you are willing to part it out. If you don't want to part out, what would you want for the complete intake. PM me.