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Hot Rods fuel return line ?

Discussion in 'The Hokey Ass Message Board' started by scotty t, Oct 9, 2018.

  1. Lets discuss fuel return lines. Through my reading and talking to other car guys it seems like a fuel return line may be a good addition to an old car. I personally don't have an educated opinion yet. My area of concern is a street car with carburetor, mech. or elect. fuel pump. Percolating and vapor lock seem to be reasons for a return line. I have a 1969 blah blah car with a factory return from the fuel filter. I also have a mechanical fuel pump with a provision for a return line, and a Holley pressure regulator with the same provision. SO do we need them? If so how should they be plumbed? Thanks!
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,714

    squirrel
    Member

    I've had decent luck using a pump with a return line, on stuff with 60s-70s engines swapped in. Just run a 1/4" line from the return fitting, back to the tank. You can maybe solder a short piece of 1/4" steel line through a hole in the sending unit, in the mounting surface.
     
  3. On my 56 chevy I've got a new 3/8 line to replace the 5/16 line, can i just reuse the original line for the return? or does it need the restriction of a smaller line? I like your idea to solder a line to the sending unit.
     
  4. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,187

    Boneyard51
    Member

    Chrysler back in the eighties, had a fuel return line from the filter , police package cars , anyway. Seemed to help flooding, which has always been a problem with Chrysler products.


    Bones
     

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 46,714

    squirrel
    Member

    I expect you could use a 5/16 return line. Bigger usually isn't a problem. The restriction is in the pump itself, not the size of the line.
     
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  6. blowby
    Joined: Dec 27, 2012
    Posts: 6,800

    blowby
    Member
    from Nicasio Ca

    First hand experience: My SBC daily (old Blazer) has a return line. Fuel pump went out. Had a new one on the shelf without a return line fitting. Put it on and plugged the return hose. Went from an immediate starter hot to taking 5 or more seconds of cranking when hot. Big difference. Squirrel ^ gave me the part no. for a filter with a return fitting. Back to fast starting hot.
     
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  7. 325w
    Joined: Feb 18, 2008
    Posts: 5,356

    325w
    ALLIANCE MEMBER
    from texas

    Yes you can. Did on a 54 Chevy with TBI
     
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  8. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 6,765

    Bandit Billy
    ALLIANCE MEMBER

    I always plumb the same size return and delivery lines. Most HP electric pumps and regulators with a return line require it.
     
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  9. big duece
    Joined: Jul 28, 2008
    Posts: 5,984

    big duece
    Member
    from kansas

    Whether one carb or several, a return at the carb (or last carb) will help keep fresh cool fuel recirculating. I would think just having a fuel pump with built in return would not have as much benefit. The fuel from the pump to the carb is still subject to under hood heat and dead headed on needle and seat. On my 4x2 setup, I will have a 1-3 lb regulator before the first carb, and small orifice in the fitting of the last carb to bleed off pressure once the engine stops. Its a barb fitting with the end tapped for a stromberg jet. thumbnail (22).jpg thumbnail (21).jpg thumbnail (9).jpg The entire time, cool gas is circulated past the bowls and returned back to the tank. Orifice size is .060
     
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  10. My next project is a dual quad Hemi with an electric pump so that info is quite useful!
     
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  11. big duece
    Joined: Jul 28, 2008
    Posts: 5,984

    big duece
    Member
    from kansas

    Another pic of a engine with a typical 4150 style carb, regulator can be before the carb or after. null_zps31feda6c.jpg
     
  12. DFAABC44-FB43-4D87-9AD3-75801FE13B8E.jpeg Big Duece, I started to mock up some fuel lines on a sbc that look a lot like yours. How is it working for you? Also I’m thinking a fram G15 filter under the regulator might work.
    Pay no attention to the wonky green line, remember mock up!
     
    Last edited: Oct 9, 2018
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  13. big duece
    Joined: Jul 28, 2008
    Posts: 5,984

    big duece
    Member
    from kansas

    Have not ran fuel in them yet, but Jim Inglese told me how to plumb his setup. I thing your on the right path, maybe move the fuel press gauge to the regulator to simplify the looks. If you can tie both bowls together and return off the rear bowl, should work for you. The size of restriction inside the return line does not have to be exact, in any way. It just takes pressure of needle and seat once pump shuts down. Without the restriction, fuel pressure would probably drop on the gauge. May have some adjustment to regulator depending on size of restriction.
     
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  14. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,926

    jimmy six
    Member

    image.jpeg I tried to run one yrs ago and had trouble starving the carb. Recently I dug it back out and down loaded the instructions from AeroSpace Industries and tried again. (There are 4 fittings on it) I copied them exact and with a full carb the pump at 5psi the return line flowed an unbelievable amount back to the tank ( I could look right into the tank and see it). I then took a feed line from front bowl, added an extension to it and turned on the pump again. The fuel from the pump flowed out that line and none went back to the tank. I then made a fitting with jet in it an added it to the extended line. This time the fuel shot out the jet, the pressure held at 5 and the return line from the reg flowed fuel back to the tank.
    I'll find out next week at El Mirage if I did every right but I finally believe I've got the plumbing correct. One point, from them was the return line was to be the same as the feed line. I didn't follow as I use a -8 from the pump and -6 back to the tank. image.jpeg
     
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  15. I like the way you used the regulator as a tee fitting, that might work well on my dual quad set up. if I'm seeing things correctly you have the gauge on the return line?
     
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 46,714

    squirrel
    Member

    you can get pretty carried away with this stuff...but all you really need is a mechanical pump, with a return line. No need to make the return line as big as the feed line with a mechanical pump, as it only returns a little bit of fuel.

    don't make it more complicated than it needs to be. This setup works, was used on millions of production vehicles, it's cheap and easy, etc.
     
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  17. I do tend to over think things.
     
  18. big duece
    Joined: Jul 28, 2008
    Posts: 5,984

    big duece
    Member
    from kansas

    I agree. Looks like the gauge is mounted on the pressure side, I believe the return line comes out the bottom.
     
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  19. carbking
    Joined: Dec 20, 2008
    Posts: 2,859

    carbking
    Member

    The easy way is to acquire an inexpensive 3-line fuel filter from your FLAPS.

    Fuel inlet and fuel outlet should be the same size, the "vapor return" outlet should be one size smaller. Place right at the carb.

    I have personally never had an issue using the above.

    Jon.
     
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  20. Beanscoot
    Joined: May 14, 2008
    Posts: 1,557

    Beanscoot
    Member

    My off topic truck has a fuel return, with a restriction in the return fitting at the fuel pump. The gas tank is rusty, and despite having a sediment bowl and inline filter, I have occasionally starved for fuel. Then I would plug the return and be able to carry on.
    The return only diverts a small percentage of the pump's output, but with a marginal system that's enough to cause one to fail to proceed.
     
  21. Screenshot_20181006-185821.jpeg

    I cured my vapor lock plague a long time ago by installing a mid 1980s AMC fuel filter on my Studes near the carburetors.
    The tiny orifice in filter return fitting keeps the hot fuel moving slowly along so the gas does not boil, and it does not overtax any stock fuel pump.
    The nice thing about this low cost method is that you dont actually have to add a real return fitting to the fuel tank.
    As long as you install a tee at or near the tank fuel outlet, the return fuel has plenty of time to cool before returning to the pump flow. As long as the fuel stays moving slowly it will never stop in one place long enough to boil.
    After being plagued with vapor lock every spring when the gas station winter fuel mix meets a hot day, I havent had vapor lock in many years after I put in this AMC fuel filter.

    WHY BE ORDINARY ?
     
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  22. squirrel
    Joined: Sep 23, 2004
    Posts: 46,714

    squirrel
    Member

    33041 is the Wix number for that return filter, with 3/8" fuel line

    33040 with 5/16" lines
     
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  23. That is pretty much how my o/t car was plumbed from the factory, i have had minor problems with hot starting but that could be a tune up issue.
     
  24. I just got off the phone with Holley tech line, i found out my mock up won't work as is. The center lower port is return only.
    [​IMG]
     
  25. So your return doesn't dump into the tank it is tee'd into the supply line near the tank?
     
  26. This thread was meant to get a discussion started about return lines not just my personal car, so if anybody has anything to add to the thread please do. And i really do appreciate all the help.
     
  27. yep Scotty T,
    I got lazy one day and decided to quick-rig one setup, and add an actual fuel tank dump-port later.
    Add ing a tee at the tank was intended to stall for time until I could "do it right", but it worked just as well as the "correct" one that I expended a lot of work on to actually add a tank fitting the "correct" way.
    the mission is to allow the return fuel to cool along the way to the rear, then reintroduce it to the fuel line heading to the front.
    I agree that this method does not have all of the bigger cooling-capacity of actually dumping fuel into the tank itself, but it has "plenty-enough" cooling :) to completely stop my previous vapor lock probs.


    WHY BE ORDINARY ?
     
    Last edited: Oct 10, 2018
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  28. big duece
    Joined: Jul 28, 2008
    Posts: 5,984

    big duece
    Member
    from kansas

    You would have to use a regulator that is not of the return Style, and have the inlet at the bottom, two exit ports on the left and right.

    Sent from my SM-G900P using The H.A.M.B. mobile app
     
  29. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,821

    Blues4U
    Member
    from So Cal

    I'd place the filter on the other side of the regulator, I believe it will filter better at a lower pressure.
     
  30. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 678

    TrailerTrashToo
    ALLIANCE MEMBER

    Consider putting the filter before the regulator to keep the crap out of the regulator.
     

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