Fuel return line

[ksechler]

I have a 280z that I am going to put triple webers on.  In the course of my restoration I had to completely redo the fuel lines.  The plumbing had been a real pain and bending 5/16" stainless precisely isn't easy.  I have bent the supply, return and vent lines, but I can see where I really need a return line anymore.  I have an electric fuel pump and a pressure regulator.  Can't I just go to the fuel rail after the regulator and be done with it?  Any help is appreciated.

[RyanT67]

Lots of people deadhead their fuel line at the carbs, no return line.  The issue with doing so is that it means the carbs won't be getting cool fuel fresh from the tank, but instead fuel that has sat in the fuel line, backed up and warmed up.  Also, most electric fuel pumps aren't happy with a dead headed system, as they will be overworking themselves trying to push fuel where it can't go.  This could lead to premature pump failure, and will definitely lead to a noisy fuel pump.  My Holley Red fuel pump makes a hellish noise, a very loud buzz that never goes away when driving - it wouldn't do so with a return line.  

Do it once, and do it right.  When I eventually redo my fuel lines, I will plumb in a return and I will put in a bypass regulator after the carbs.  This essentially means that the carbs will get constant pressure to them with no drops, and any excess will bleed off into the return line after the carbs.  Much better way to do things.    

[RyanT67]

Tank  -> Fuel filter -> Fuel pump -> Fuel filter -> Carb -> Carb -> Carb -> Fuel pressure regulator -> Tank

[Reverend]

Why the pressure regulator is after carbs, shouldn't it be before them?

[HaZmatt]

Why the pressure regulator is after carbs, shouldn't it be before them?

 

If you are running a return line, the regulator goes after the carbs. 

[Mark Maras]

I'm with the Reverend on this one. Logically, to me, it would seem as if the reg. would go before the carbs. I don't doubt what you say, but I'd still like to know why it goes after the carbs. Anyone?

[HaZmatt]

You could probably run it either way, but I read something about it keeping fuel pressure in the carbs at higher RPMs when placed after the carbs.

[RyanT67]

I know it sounds counter-intuitive to regulate after the carbs, it took me a little while to wrap my head around it when I first read up on it.  

As I understand it, it's about flow.  Most fuel pressure regulators work by adjusting a screw that opens/closes flow through a valve.  This works great for adjusting the fuel pressure, but it greatly restricts the flow of fuel.  Now, I'm making up these numbers as an example, but if your pump is putting out 97 GPH at 7psi, then after a regulator set to 3.5 psi there might only be 40 GPH getting through.  This backs fuel up and puts strain on the pump, and it means that there might not be enough flow to properly supply the carbs at WOT.

By placing a bypass regulator after the carbs, the carbs will get the full 97 GPH flow of fuel, and any pressure beyond 3.5 psi will go off into the return line.  You still get your fuel pressure regulated, but there will be more flow, and more fresh fuel, with less chance of pressure dropping at high throttle when you have your foot down.  

Regulate before or after, both ways work, but after works more effectively.  

[HaZmatt]

^^^ What he said

[Mark Maras]

 Thanks for that concise explanation. It makes perfect sense now. Proof you can teach an old dog new tricks.

[Reverend]

Dayum son. That might make sense. I'll have to try that. I have problem with my carb nr 3, most likely related to fuel.