Fuel return line

[KZ900Jim]

My sons '79 wag is now officially a '72 as far as the CA DMV is concerned..😏

We have an edelbrock 2131 and a 600 cfm Holley to sit on top.

My question is, can I abandon the fuel return line? I realize its part of the emissions requirements but that's not a concern anymore.

[SIUADOG]

Also curious, as we are swapping intakes this weekend. Hopefully someone will be able to clarify exactly what that line is for, vapor or fuel.

[TexasJ10]

The fuel return line is just that. Any excess fuel and pressure not required by the carb is returned to the tank via the fuel filter setup. I suspect that it takes a lot of pressure off the needle since the fuel pump is going to keep trying to send fuel to the carb whether needed or not. I don't know if the fuel pump can regulate that by itself, but I don't think so. The fuel vapor line from the tank is a separate line with a connection in the engine compartment that goes into the charcoal canister. Personally, I would use the return line for its intended purpose.

[rang-a-stang]

The 1979 Service Manual says (on page 1J-6)
Fuel Return System:
All models use a fuel return system to reduce the possibility of high temperature fuel vapor problems....
The special fuel filter has an outlet nipple connected to the fuel return line. The fuel return line is routed to the fuel tank, where it attaches to a nipple on the fuel tank sending unit. During normal operation, a small portion of fuel is returned to the tank. During periods of high under hood temperatures, vaporized fuel is returned to the tank and not passed through the carburetor.

So, in other words, the return line is there to prevent vapor lock. My return line has not been hooked up (but is plugged) in over a year on my truck with no ill effects (including passing a smog check). You'll notice almost all Carb'ed hot rods do not have return lines, either.

So, unless you are going to use the stock fuel filter, plug the return line as close to the tank as possible and remove the rest of it. Without the stock style fuel filter, I am not sure how you could hook up the return line anyway.

BUUUuuuttt know you are more susceptible to Vapor Lock without it. In Camarillo it's not an issue (we almost never get over 100 degrees) but I am not sure how Hayward weather would effect it.

[TexasJ10]

That "small" amount of fuel is actually quite a bit. You can hear it returning to the tank if you put your ear to the tank even at slow idle. It is a very steady flow. Do you need it? As pointed out, cars ran without them for years, but I would still use it if available.

Rang a Stang, good info on the vapor lock issue. It makes sense it would help keep that from happening.

[itselliot]

Return line

I JUST, this week, fired up my freshly built 401.
Has a Holly 4160 , 600 CFM 4 bbl...I omitted the return line in my build...."why should I " I thought..................then upon the first "in Vehicle" start up , the fuel just pressured it's way past the needle and seat in the Holly and started to spit up through the bowl Vents.
I have just last night completed the installation of a new return line using the standard AMC return port type fuel filter.
I used a temporary, clear fuel line in a section near the engine to view the flow. There is a significant amount of fuel being returned to the tank!!!

Its my understanding that Holly's are not able to handle more than 4-5~Lbs of fuel pressure.....So regardless of emissions, I find that the return line is necessary. One could use a pressure regulator I assume, but that would not help with the vapor lock issue at all.

[J20 project]

You are dead on w/ that itselliot...


J20

[kansasboy001]

One could use a pressure regulator I assume, bit that would not help with the vapor lock issue at all.

If a bypass (return) type pressure regulator is used it accomplishes the same thing as the factory return filter only precisely meters the pressure. The old vapor lock kits that used to be sold in the full size jeep magazine used a bypass regulator

[itselliot]

If a bypass (return) type pressure regulator is used it accomplishes the same thing as the factory return filter only precisely meters the pressure. The old vapor lock kits that used to be sold in the full size jeep magazine used a bypass regulator

I have not heard of a "bypass" type regulator........Hmmmm
Always assumed that a regulator would just back up the mechanical fuel pump causing it to work harder and fail sooner. I need to go shopping now.

[kansasboy001]

A bypass regulator has a 2nd outlet that connects to a return line to the tank. Instead of backing up the pump it returns the excess pressure to the tank even more than the stock filter setup. This is the one I use

https://www.summitracing.com/parts/qft-30-900qft?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-quick-fuel&gclid=CjwKCAiA47DTBRAUEiwA4luU2QrLVDYhxc4WljWwn3FcUCu8CAFf7A8R-wH0AnBzrYzCPoLXtOXLwBoCoD0QAvD_BwE

[Don S]

..

Each blend of gasoline has it?s own temperature vaporization point. Plus there are summer and winter grades. Note. The vaporization point drops to a lower temperature as the pressure drops, they are related. Some blends of gasoline will vaporize at 145 degrees at sea level. Heat from the engine compartment is routed toward the fuel tank. Fuel pumps get hot. Fuel tanks are close to hot road surfaces. This all helps bring the fuel up closer to it?s vaporization point.
The fuel return line is your friend. It can send the vaporized gasoline back to the tank where it condenses back into usable gasoline. The three way filter should be angled upward with the return nipple at the highest point. The return line should be routed away from heat sources as it can add to the temperature of the fuel in the tank.
In 1970 I was a Pontiac and Rambler salesman The 1970 Pontiac Bonneville?s came with the three way filter. Ever store gasoline in an open can at ambient temperatures well below vaporization point? Somehow it disappears leaving just the fuel additives!

It worked for me.. Don S..

[FSJunkie]

With everyone whining about carbureted cars with vapor locking and other vapor-related issues in hot weather and thinking electric fuel pumps are the heaven-sent solution, I find it silly that anybody would want to get rid of the fuel return system. Even many more modern fuel injected cars have some kind of fuel return system to keep the fuel in the lines always circulating.

[EasTXJEEPER]

My 83 Cherokee 360 with a 600 cfm Edelbrock was starved for enough fuel until I disabled the fuel bypass line.
Crusin just wasn't any fun when my Jeep couldn't pull even the slightest grade. If the carb Bowls aren't full because of low fuel volume due to pumped fuel going back to the tank. I FIXED IT The Cheapest Way Possible

[wiley-moeracing]

good for you, glad removing it worked for you, but I still know a return line is a good thing to help with vapor lock issues unless you set your system up to run a electric pump with a regulator and then you can still run a return line.

[Maherpmj]

I JUST, this week, fired up my freshly built 401.
Has a Holly 4160 , 600 CFM 4 bbl...I omitted the return line in my build...."why should I " I thought..................then upon the first "in Vehicle" start up , the fuel just pressured it's way past the needle and seat in the Holly and started to spit up through the bowl Vents.
I have just last night completed the installation of a new return line using the standard AMC return port type fuel filter.
I used a temporary, clear fuel line in a section near the engine to view the flow. There is a significant amount of fuel being returned to the tank!!!

Its my understanding that Holly's are not able to handle more than 4-5~Lbs of fuel pressure.....So regardless of emissions, I find that the return line is necessary. One could use a pressure regulator I assume, but that would not help with the vapor lock issue at all.

Actually Holley recommends 5-7 psi for proper fuel pressure. Been running a TA670 at that pressure with no problems with flooding or vapor lock without the return line in hot AZ summers. Using a Carter E-pump