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  1. #1
    Join Date
    May 2008
    Posts
    20

    Default Fuel filter not full - potential vapor lock?

    Do you know how full a fuel filter should look during idle, 1900 RPM cruise or full throttle? I recorded the vid linked below showing both fuel filter (on left half of screen) and fuel bowl (sight glass) levels. I sent the vid starting at 8:50 when vehicle's warmed up & we go WOT to show what's going on. (If you want to see the fuel levels when the car was cold, that's at the 0:00 start of the clip.)
    https://youtu.be/Bz2W80TD-cA?t=530



    The car runs great in cruise & WOT, but when it was over 85F outside recently, I noticed the air/fuel ratio at idle would creep from 15:1 to mid 17s when idling or off-throttle decel. Which is why I've started looking into potential vapor lock since the car will also drain the bowls if parked for a week after being parked when warm.


    Figured I should ask you if this behavior is normal for a car with the Carter high-flow mechanical pump, Demon 750 carb, and a new fuel tank & hard lines installed in 2004 (stored with Sta-bil anytime it was parked over a week).


    If it's not normal, I'll drain & drop the tank to look into whether the sock might be clogging, or whether there's a safe way to install another vent to reduce pressure (removing the gas cap will add more fuel to the filter - I've tried a new vented and a vented locking cap w/same results). Last resort might be adding an electric fuel pump in-tank and maybe a bigger (1/2") line toward the engine & use the stock 3/8" line as a return - not a fan of adding complexity, running wires & relays if we don't have to, as I'd like to stay carbureted.
    https://www.youtube.com/watch?v=5_73rDt7z1k

    Thanks in advance for ideas & wisdom you can offer.


  2. #2
    Join Date
    Sep 2016
    Location
    Bakersfield, CA
    Posts
    83
    Country Flag: United States

    Default

    I think that's normal for a fuel filter level. I also have the issue of going lean when my engine is heat soaked for a period of time. Or restarting when hot. Very annoying and I already have a fuel return line. I'm running an AED Holley 4150 750cfm, 3/8 feed and 1/4 return. I wrapped the hardline going from the pump to my carbs fuel rail in a fiberglass heat protection sleeve and also wrapped the entire fuel rail. I also run a wooden 1/2" spacer under my carb and have my heat crossover blocked.

    My next move is to put air extraction vents into my hood even though I already have them on the side of my front fenders already. I also have an airtight sealed cold air setup from my air cleaner to my hood.
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  3. #3
    Join Date
    May 2008
    Posts
    20

    Default

    Thank you - this is a huge help to know it's fairly normal.

    Although the shop that did this fuel system (which has worked well enough for 15 yrs) put the filter right at the inlet side of the Carter high-flow pump (which is nice & low, far away from header or other heat sources), I'm considering moving it to be in between pump and carb since I've read that it's better to have the fuel filter between the pump and carb.

    Or, I might get a higher-flow filter to install in the rubber line from tank to hardline, and remove the current filter.

    Trying to minimize restrictions and would like to avoid having to go to an in-tank electric fuel pump w/return lines. Seems like someone would have made a simple high-flow mechanical fuel pump with return setup by now.

  4. #4
    Join Date
    Sep 2016
    Location
    Bakersfield, CA
    Posts
    83
    Country Flag: United States

    Default

    Yeah, filters are meant for fuel to be pushed through them, not sucked through them.

    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.




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