Running a return line to fix vapor lock

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    Author Topic: Running a return line to fix vapor lock  (Read 5889 times)

    Offline msbaugh

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    Running a return line to fix vapor lock
    « on: June 12, 2012 - 04:21:32 PM »
    I just put a new Holley mechanical pump, 3/8 fuel line, a new sender unit and a Holley carb with a pressure regulator and pressure gage on the challenger. It runs a real healthy 6 1/2 then after it heats up the fuel pressure goes to 0!!  :banghead: I would like to run a return line and get a new return style pressure regulator to keep it flowing and fix the issue. The Holley tech guy I talked to says I can't run a return style regulator with a mechanical pump because of the "pulsating fuel flow". But I don't want to buy an electric pump,I like the new one I have. Can I make a return line/regulator work with the mechanical pump? Where can I buy one?
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    Offline Chryco Psycho

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    Re: Running a return line to fix vapor lock
    « Reply #1 on: June 12, 2012 - 06:23:38 PM »
    The 70 system used a return line connected to the vapor separator . you could adapt that system
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    Offline msbaugh

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    Re: Running a return line to fix vapor lock
    « Reply #2 on: June 12, 2012 - 10:21:44 PM »
    Are you aware of a pressure regulator that has 3 fittings applicable for mechanical pump setups?
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    Offline BS CUDA

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    Re: Running a return line to fix vapor lock
    « Reply #3 on: June 12, 2012 - 10:27:56 PM »
    Holley 12-803BP with 3/8 pipe in out and a return. Or the Holley billet series - I just ordered the 12-845    -8 in/ out and -6 return. Slurp  :cooldancing: I am also running a high perf mechanical and have been told it will be fine - I will report early next week with any luck.
    « Last Edit: June 12, 2012 - 10:29:50 PM by BS CUDA »
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    Offline solarguy

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    Re: Running a return line to fix vapor lock
    « Reply #4 on: June 13, 2012 - 07:58:13 AM »
    I'm curious,  does the car stall when fuel pressure drops to zero?  If not, I would suspect that the gauge, especially if liquid filled, is inaccurate. 
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    Offline msbaugh

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    Re: Running a return line to fix vapor lock
    « Reply #5 on: June 13, 2012 - 11:07:00 AM »
    The gage could be off, but I doubt it. The pressure will go to 0 if I sit and idle for too long. It has stalled once before on a very hot day after it was all warmed up. I sat and let it cool off for a while and was able to start it back up and drive home. Where it's really evident is after a long cruise it will sometimes sputter upon WOT. Like its clearing the vapor out of the system.

    I suspect that the carburetor isn't using all the fuel supplied from the pump, so it gets too hott and drops the pressure... Maybe some jetting and carb adjustments will help but I think a return line will be the only solution, especially with the hot summers here in Houston. My drives are generally short enough that its not a real troublesome issue but it still would be nice to be confident that it will be fine on long cruises in the heat
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    Offline msbaugh

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    Re: Running a return line to fix vapor lock
    « Reply #6 on: June 13, 2012 - 11:21:11 AM »
    Quote from: BS CUDA on June 12, 2012 - 10:27:56 PM
    Holley 12-803BP with 3/8 pipe in out and a return. Or the Holley billet series - I just ordered the 12-845    -8 in/ out and -6 return. Slurp  :cooldancing: I am also running a high perf mechanical and have been told it will be fine - I will report early next week with any luck.

    That's intersting.. It says on volleys application manual that the 12-803BP is not to be used with mechanical fuel pumps! If you don't mind, let me know how it works out for you.. There's got to be one out there that'll work
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    Offline BS CUDA

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    Re: Running a return line to fix vapor lock
    « Reply #7 on: June 13, 2012 - 08:33:27 PM »
    Quote from: msbaugh on June 13, 2012 - 11:21:11 AM
    That's intersting.. It says on volleys application manual that the 12-803BP is not to be used with mechanical fuel pumps! If you don't mind, let me know how it works out for you.. There's got to be one out there that'll work
    Well I always seem to learn the hard way!! Too bad your post wasn't a day earlier(prior to me ordering the regulator without the pump) and perhaps I should have consulted Holley. Now everyone I talk to who was so sure of the bypass regulator working in my set up is unsure. They somewhat question the pulse movement of a mechanical pump but are unsure why. Perhaps not enough volume to open the bypass? Not enough pressure to bypass and keep car idling?? I am going to try it to answer these questions. What could go wrong  :bigsmile: If I have to purchase an electric HP Billet pump to go with the reg it won't be the end of the world - just an excuse to spend more cash on the car.
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    Offline msbaugh

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    Re: Running a return line to fix vapor lock
    « Reply #8 on: June 13, 2012 - 11:16:53 PM »
    Quote from: -Sledgehammer- on June 13, 2012 - 08:45:47 PM
    do you have a spacer plate to get the carb off the intake.

    Nope! But I blocked the heat crossover... Would a spacer make that big of a difference? I guess it's worth the try, I'm short on room though that's for sure, I'll have to see if one will fit
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    Offline msbaugh

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    Re: Running a return line to fix vapor lock
    « Reply #9 on: June 14, 2012 - 12:30:31 PM »
    I rear a few articles in mopar mag where they dyno tested using a large spacer and it improved power! So that could be another reason to give it a try
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    Offline Chryco Psycho

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    Re: Running a return line to fix vapor lock
    « Reply #10 on: June 14, 2012 - 03:06:50 PM »
    At some point the gains have to diminish , the higher you push the carb the more restrict the air cleaner becomes !!
     So at some point you have to add a hood scoop or like new cars turn the carb sideways a draw cold air from the front of the car !!
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    Offline 73EStroker

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    Re: Running a return line to fix vapor lock
    « Reply #11 on: June 16, 2012 - 08:34:28 PM »
    If you are running a bypass regulator system then first you require the same size line back to the tank as a return. Yes it cures most of your heat soak/vapour lock issues. You also need to be feeding about 15psi into the BP regulator, which you should have located fairly close to your carb, and one other advantage is to insulate the fule lines inside the engine compartment but especially where the fule lines (return and supply) run adjacent to the headers down by the front frame rail. It can be a 100ºF and my only issue is after shutting down she heat soaks a bit around the carb but a quick squirt from the next light fixes the issue. I have the BP setup with a Mallory 110 pump (18psi) and zero issues in 2 years.
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    Barry (Salmon Arm)
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