fuel line question

[mossy74]

I'm restoring my SBC 240z at the moment and was looking at getting the brake and fuel lines restored and I noticed the fuel return line was cut and clamped off, is this normal?

[deja]

If its a carb engine with a mecanical pump you don't need the return line. My old carb engine had a return fitting on the fuel filter which was hooked to the return fuel line. I have no idea if it actually did anything useful.

[grumpyvette]

I TOTALLY disagree!

YES IN MOST CASES A CARB APPLICATION CAN RUN WITH NO RETURN LINE , BUT YOU WON,T TEND TO GET CONSISTANT FUEL FLOW VOLUME AND PRESSURE AT THE CARB WITHOUT A RETURN LINE STYLE FUEL PRESSURE REGULATOR, and you would be amazed at the number of tunning issues that are avoided with a decent return style fuel pressure regulator installed in a fuel supply line system , like inconsistant float levels, seemingly non-working fuel metering at idle, and high rpm lean or rich conditions.The manufactureres would NEVER spend the money on fuel return lines if it was not almost mandatory to getting the car to run consistantly and pass emmission testing under some conditions.

its kind of like carring a spare tire , a jack in the trunk,or wearing a bullet proof vest, 90% or more of the time you could get bye without them, but under some comnditions not having them becomes a HUGE problem

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=211

Edited April 13, 2009 by grumpyvette

[deja]

Interesting, makes sense. I bow to your expertise, ya learn something everyday. But this is talking about electric fuel pumps. Can I assume the same thing would apply to a stock engine mounted mechanical pump?

 

I TOTALLY disagree!

YES IN MOST CASES A CARB APPLICATION CAN RUN WITH NO RETURN LINE , BUT YOU WON,T TEND TO GET CONSISTANT FUEL FLOW VOLUME AND PRESSURE AT THE CARB WITHOUT A RETURN LINE STYLE FUEL PRESSURE REGULATOR, and you would be amazed at the number of tunning issues that are avoided with a decent return style fuel pressure regulator installed in a fuel supply

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=211

[mossy74]

Ok, looks like i will need a return line then, it was running a mechanical pump before I stripped the car down but since I am repositioning with a JTR kit I will be going with an electric pump, thanks.

[lovemstr]

I agree with DEJA, if you are running a mechanical fuel pump on your sbc you dont need a return line.

[rsicard]

Electric or mechanical fuel pump, it is always advisable to have a pressure regulator and return fuel line.

[Pyro]

yes, much better to have a return system. keeps the gas cool and pressure constant. However, if the pump isn't designed to run a return then don't run one. The pump needs to put out more pressure that the fuel system needs then the return line lets the excess go back to the tank to regulate the pressure. if a pump can't make more pressure than required then no return should be used.

 

and about the stock sbc pump....

some mechanical pumps for sbc require a return and others don't. typically earlier sbc pump don't use return a line but later model pumps do require them to bleed off the excess pressure. If a 75 mech pump is used without a return , it will over power the needle and seat of a carb.

 

Back to the 240.

I have run my 240 with and without the return line line. I really didn't notice much difference. However, I was only 20, and I didn't notice as much back then. I would use the return line if you are using the stock pump. Just make a new clean cut on the return metal line and run a longer rubber gas line to the meal line. You don't need barbs, as the pressure is very low, just make sure to match the ID of the rubber hose to the OD of the metal line as close a possible.