Ideas on running a fuel return line

-
mtandrews

mtandrews

beware the Ides of March
FABO Gold Member
Joined
Jun 2, 2010
Messages
16,949
Reaction score
2,633
Location
Wilson County, Texas
here's the layout, 72 Duster with a mild 318 replacing the slant 6 (had charcoal canister which is long gone) new tank and sending unit with a 3/8 out and 5/16 in, eddy 1406 carb and a stock style replacement fuel pump. Daily driver in the making.

I'm currently bending up 3/8 line and plumbing in a FRAM spin on filter to replace the stock 5/16 feed line and being I want to run a return now I'm trying to figure out how. I can't remember where I read it but I read that plumbing a return line will help fix vapor lock problems which would be great because I live in Texas and sometimes it gets kinda hot(!). Had serious vapor lock problems in the past in my 68 Fury (no return system). I'm thinking the smaller nipple on the sending unit was for the vent or something to do with the charcoal canister. Do I need to need to add another nipple to the sending unit or can I use this as a return? Adding another nipple wouldn't be a problem if necessary. Where/what should I tap for a return? It's a single feed Eddy carb. Figure I'd throw this up while I'm out here bending and flaring...
 
the only reason i know of running a return line is if u have a high volume/pressure pump and u only want 7psi, so the regulator is bleeding off what u dont need and heading back to the pump.

but i mite be able to see where that might work!

think we ran 1/2" up and 3/8 back but i'll check tomarrow
 
use the stock line as the return. run the 3/8s line to the carb with the regulator after the carb inlet and it wont vapor lock. use the vent for the return and run a vented cap.
 
run the 3/8s line to the carb with the regulator after the carb inlet
I'm trying to visualize... maybe I need to get some rest first, been a long day.
 
I'm a HUGE believer in vapor return systems. First one I ever saw was on my '70RR 440sixpack. If you are running new 3/8 line, you can either use your old existing 5/16, or if you had a vapor can, it SHOULD already have a second line back?? to the tank, you could use that.

Wix makes a couple of filters, one 5/16, one 3/8, and I ALWAYS have a hell of a time looking them up. They have a 1/4" output for the vapor, which must be mounted "up." the filter can either be mounted vertically or horizontally, so long as the 1/4 fitting is "up."

I believe, Wix no 33040, 33041, same no. from NAPA without the first "3"
 
I am doing the same, but for a high-pressure fuel pump feeding a TBI. The fuel sender I recently got has a 3/8" outlet and 1/4" return. I am using the factory 5/16" tube for the return. It sounds like your sender is different since your small nipple was for a charcoal canister. Surprising for 1972, since I thought those started in the late '70's. Perhaps yours was a CA car.

Re vapor lock, interestingly newer engines (~2000+) don't have a return line. Pump bypass is done in the tank, with only a single tube to the engine. I understand that is an EPA reg to keep the gas in the tank cooler & limit boil-off. The higher pressures for MPFI (>50 psi) must prevent vapor generation in the tubing.
 
yes the car had a charcoal canister which is long gone and I understand that I can use the old feed line for a return, what I'm trying to get a grasp on is the plumbing up front to initiate the return...
 
mtandrews said:
yes the car had a charcoal canister which is long gone and I understand that I can use the old feed line for a return, what I'm trying to get a grasp on is the plumbing up front to initiate the return...
Click to expand...

That's the simplest part of the whole deal. Use one of the filters I mentioned, or a similar device. Those two Wix numbers have a dedicated return fitting WITH THE ORIFICE already in the filter. Just install the filter as close to the carb(s) as practical, 1/4" line "up" and plumb that fitting into your return tube. easy.

This constantly returns a small amount of fuel to the tank, helping to reduce heat buildup in the upcoming fuel--because it's always moving, and provides a pressure relief on shutdown. Any vapor trying to form in the output side of the pump simply builds a little pressure and forces fuel back through the orifice to the tank.

A picture that I "stole" somewhere:

http://media.photobucket.com/image/%2522vapor return%2522/h2ospout/IMG_0885.jpg


Here's an example of what is most probably a GM pump, with a vapor return off the bottom of the pump. This tube extended to the top of that big can, and had an orifice either at the top or bottom. I never figured they would work as good as one closer to the carb:

http://articles.directorym.com/Images/Image.aspx?ParagraphId=208


Another thing that is helpful IF vapor is the problem, is a rear-mount electric pump. This is because a stock up-front pump is SUCKING on the inlet line, LOWERS the line pressure, and LOWERS the boiling point. A rear "pusher" pump, keeping the entire line system under positive pressure, INCREASES the fuel boiling point.
 
I always like havin the carburetor itself as the exchange point for the return line, but havin that filter with the return line on it is certainly better than nuthin.
 
if you run a return i would do it in the 3/8 like the supply. if you ever upgrade things you won't have to worry about that 5/16 return bottle necking things.
 
abodyjoe said:
if you run a return i would do it in the 3/8 like the supply. if you ever upgrade things you won't have to worry about that 5/16 return bottle necking things.
Click to expand...
my "plan" :poke: was to use the original feed as the return as I have already ran a new 3/8 line from the tank to the pump. I got a new sending unit that is 3/8 feed so I'll run a hose from the old feed to the return on the new sending unit. I guess I'll cap off the other tank line that ran to the charcoal cannister which has been put in the Round file :glasses2:
 
BillGrissom said:
I am doing the same, but for a high-pressure fuel pump feeding a TBI. The fuel sender I recently got has a 3/8" outlet and 1/4" return. I am using the factory 5/16" tube for the return. It sounds like your sender is different since your small nipple was for a charcoal canister. Surprising for 1972, since I thought those started in the late '70's. Perhaps yours was a CA car.

Re vapor lock, interestingly newer engines (~2000+) don't have a return line. Pump bypass is done in the tank, with only a single tube to the engine. I understand that is an EPA reg to keep the gas in the tank cooler & limit boil-off. The higher pressures for MPFI (>50 psi) must prevent vapor generation in the tubing.
Click to expand...

At least in Calfornia, charcoal canister usage actually dates back to the very early 70s.

When I moved to California in the mid 80s, I took my, from out of state, LA motored '71 Dodge van to a place just outside Sacramento for a smog test. It passed the sniffer with flying colours, but the guy doing the test told me the van had failed for missing some of the required smog equipment items, specifically the charcoal can and a preheat tube to the air cleaner inlet. After having spent the better part of a day at a pick your part yard and a couple more working on the van to install a charcoal canister and lines, wrapping the air preheat stove from a slant six exhaust manifold around a header tube to run the auto parts store bought paper tube up to the snorkle of the newly installed small diameter Buick V6 air cleaner disguising the 340's four barrel (and making it look much more like the original two barrel 318 that had once resided there), I was more than a little incensed. I told him get his lazy *** under the rig and look, and not to assume that just because it had headers that the stuff was missing.

Needless to say, the smog test was passed with no more drama and nary another word said.
 
abodyjoe said:
if you run a return i would do it in the 3/8 like the supply. if you ever upgrade things you won't have to worry about that 5/16 return bottle necking things.
Click to expand...

But you gotta run some kinda restriction in the return line or there's be hardly no pressure.
 
Ok, I'm slightly confused. If I run an electric pump at 7 psi with a regulator(using an 850 thermoquad) pushing from back by the tank do I need to do anything with the return line? I was going to put a filter on the return line up by the carb and just leave the other end of the filter open??????
 
I don't see a problem dustoff, but I'm not grasping what you're saying about putting a filter in your return line...
 
You must log in or register to reply here.
-

Back
Top