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  #1  
Old 10-17-2017, 10:15 PM
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KZ900Jim KZ900Jim is offline
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Fuel return line

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.
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  #2  
Old 11-01-2017, 12:40 PM
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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.
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Old 11-01-2017, 12:52 PM
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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.
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  #4  
Old 11-02-2017, 12:35 AM
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rang-a-stang rang-a-stang is offline
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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.
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Old 11-02-2017, 08:03 AM
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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.
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* 1981 stepside, 360, 727, 208, almost stock daily driver.
* 1982 Laredo j-10, 360, 727, in rough shape and in the process of being rebuilt with 401, NV4500, Klune,
. NP205,d60 front, d70 rear, fender work and minimal lift. It will probably take 10 years
* 1973 jcab mounted on 1983 j20 frame. 360/t18/208 d44/d60. Almost completed
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  #6  
Old 01-24-2018, 08:02 AM
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itselliot itselliot is offline
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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.
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Last edited by itselliot : 01-25-2018 at 07:54 AM.
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  #7  
Old 01-24-2018, 12:29 PM
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You are dead on w/ that itselliot...


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  #8  
Old 01-24-2018, 05:41 PM
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Quote:
Originally Posted by itselliot
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
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  #9  
Old 01-25-2018, 07:57 AM
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Quote:
Originally Posted by kansasboy001
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.
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'78 J-20 401 Q/T not quite stock anymore....Frame off Resto Mod..Super Cab nearing completion.
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  #10  
Old 01-27-2018, 03:07 PM
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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=CjwKCAiA47DTBRAUEiwA4luU2QrLVDYhxc4WljW wn3FcUCu8CAFf7A8R-wH0AnBzrYzCPoLXtOXLwBoCoD0QAvD_BwE
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  #11  
Old 01-28-2018, 03:51 PM
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..

Each blend of gasoline has itís 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 itís 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 Bonnevilleís 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..
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  #12  
Old 01-29-2018, 12:36 AM
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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.
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