[stu72]

Hello all,
I am going to plumb the return line from the fuel pump back in service. I am running a Holley 12-837 pump with the two outlets. My question is should the return line fittings be restricted or wide open? My thinking is restricted.
Thanks

[tjs72lemans]

It seems to me they were all free flowing and open.

[stu72]

Originally Posted by tjs72lemans

It seems to me they were all free flowing and open.

Are these factory style pumps or aftermarket?

[TedRamAirII]

You never want a restriction on a return line.

[Tom Vaught]

Never restrict the fuel line going back to the tank, you want the fuel pressure regulator to be the "controlling" device.

Now some mechanical fuel pumps worked with a very small VAPOR restrictor in a vehicle fuel return line to get rid of the vapors in the fuel pump chamber after the vehicle had set for a period of time in the summertime AFTER a long hot trip somewhere.
Lots of A/C equipped vehicles had this system.

This system is a "vent" to allow the mechanical fuel pump to pump liquid fuel into the carb vs hot vapors.

NO RESTRICTOR IN THE RETURN LINE AFTER A FUEL PRESSURE REGULATOR.

Tom V.

[stu72]

Originally Posted by Tom Vaught

Never restrict the fuel line going back to the tank, you want the fuel pressure regulator to be the "controlling" device.

Now some mechanical fuel pumps worked with a very small VAPOR restrictor in a vehicle fuel return line to get rid of the vapors in the fuel pump chamber after the vehicle had set for a period of time in the summertime AFTER a long hot trip somewhere.
Lots of A/C equipped vehicles had this system.

This system is a "vent" to allow the mechanical fuel pump to pump liquid fuel into the carb vs hot vapors.

NO RESTRICTOR IN THE RETURN LINE AFTER A FUEL PRESSURE REGULATOR.

Tom V.

I think I should have given more information. I am currently not use a pressure regulator with this pump. It’s only 80 gpm at 7 psi.
I am looking to vent using the return line from the pump. This being a Holley pump with two outlets. My thinking was to use the second outlet with restriction to achieve this. Is this the wrong way to go about this or should I be looking at regulators to add?
Thanks

[Tom Vaught]

Think that you have a typo there with the 80 gpm number. 80 gallons per hour is probably what you meant to type. 80 gal per minute would mean that you could take all of the fuel out of one 55 gallon drum and 50% more out of a second drum in less than a minute.

A Fuel Pressure Regulator is the way to go, even if it is a cheap Holley red regulator used with a mechanical pump as the fuel pressure could be set to 5.5 psi fuel pressure for the carb that way. Unless racing you really do not need any more fuel pressure than that to lift the fuel from the gas tank to the carb inlet.

Tom V.

[stu72]

Originally Posted by Tom Vaught

Think that you have a typo there with the 80 gpm number. 80 gallons per hour is probably what you meant to type. 80 gal per minute would mean that you could take all of the fuel out of one 55 gallon drum and 50% more out of a second drum in less than a minute.

A Fuel Pressure Regulator is the way to go, even if it is a cheap Holley red regulator used with a mechanical pump as the fuel pressure could be set to 5.5 psi fuel pressure for the carb that way. Unless racing you really do not need any more fuel pressure than that to lift the fuel from the gas tank to the carb inlet.

Tom V.

Thanks Tom, yes typo. Work with hydraulic pumps at work and always reference gpm vs gph. Lol

[Tom Vaught]

What kinds of cool Hydraulic Work are you involved with?
Production of the pumps, assembly of machines that use hydraulic pumps?
Tell us more. cool subject.

Tom V.

[stu72]

Originally Posted by Tom Vaught

What kinds of cool Hydraulic Work are you involved with?
Production of the pumps, assembly of machines that use hydraulic pumps?
Tell us more. cool subject.

Tom V.

Where I work we build vertical die cast aluminum presses. The power units use a vane pump with a piston pump with a 250 gallon tank for the smaller machines. Presses range from a 100 ton to a 1000 ton. Mostly electric rotor cores.
I had the opportunity after 18 years of machining to move onto assembly and service in the field as well installation of new presses.

[Tom Vaught]

Thanks, I bet a bunch of people are happy for your years of service with the company.

Tom V.

[stu72]

I don’t know all about that but thanks. Lol
Currently 26 years in and have had the opportunity to experience and learn a few things.

[lust4speed]

We've installed a small return line on some of the club member's cars where they have been running an electric pusher pump with a dead-head regulator and larger feed line, but didn't want the expense of changing over to a new by-pass regulator and large return line. We T the line just before entering the carb and run a line down to the original (and not used) Pontiac feed line or the original return line if there is one. We drill and tap the small -AN adapter going into the T to take a Holley #90 jet to return a little of the fuel back to the tank. It does seem to help keep the fuel moving past hot spots and also lets the pump run just a little cooler.

The original restriction in the mechanical fuel pumps I've cut open usually measure about .063" at the tip of the inner cone inside the pump chamber, but figured a little bigger was needed.

Definitely not near as good as a by-pass system, but for helping out an existing dead-head system it seems to work.

[stu72]

Interesting, I am not running a pusher pump of any sort though. Wonder how this would work with a mechanical pump only? The reasoning I started this thread about using a restricted return directory off the pump was when I purchased this pump many years ago it came with a barbed hose type fitting for a 1/4 line with a roughly.060 hole in it.
I am currently dealing with to high of fuel temp and looking to resolve them. I do need to block off my heat cross overs in the intake. Also need to reroute some fuel lines away from the driver side header.
Had some heat issues at idle but seem to have this under control now. Clutch fan took a **** and was allowing temps to climb to 195. Now back down to 180.

[lust4speed]

The mechanical pump will not have the pumping capacity of the electric pump and I'd probably stay with the return restriction that the factory used which is about the size of the existing bleed someone installed on your engine.

Included are photos of stock deep and standard pumps cut open showing the return restriction. GM did a nice job on the deep chamber pump. The inlet introduced fuel at the very top (the barrel shaped assembly) where vapor could quickly separate out and the vapor bleed is also at the very top. If there was any vapor it was the first to be pushed back to the tank, and then regular fuel would be returned. This deep setup allowed for the fuel going to the carb to go out the bottom after settling down somewhat, and the larger chamber made a nice reservoir. The added bleed system at the carb allows some fuel circulation but lacks the sophistication of the stock system.

[lust4speed]

One of the cars with the added return line was by today so snapped a quick photo to show the assembly. The Holley jet is inside the -4AN adapter fitting.