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Thread: dual feed fuel filter to single. CJ 7

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    dual feed fuel filter to single. CJ 7

    I have an 85 CJ7 4.2 L. She is being a real beast to start if i let her sit for a day.
    I looked at the filter and made sure the return line is in the 12 o' clock position.
    Seems like the fuel is siphoning back into the tank. If I crank it over A LOT she starts and runs like a peach.
    Now what I am wondering if I should go to a single feed line and plug the return.
    I'm not looking forward to dropping the tank and changing the fuel pump if that is what it is.
    Advice?
    Cheers

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    When I changed to the Holley Carb I found that the single in / out filter didn't work well and went back to the one in two out. I also believe that the fuel pump is mechanical and on the engine and not located in the tank.
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    Assuming you have the OEM carb and not a swapped in EFI system, the mechanical fuel pump is on the side of the block and not in the tank.

    Unlike EFI, a carb has a float bowl full of fuel that will start and run the engine for a brief period even with no fuel in the line. It does not require immediate fuel pressure to start unlike EFI. So, it is unlikely that fuel siphoning back to the tank is causing hard starting unless it can be siphoned right out of the float bowl which wouldn't be possible on any carb I have seen.

    I would think the hard starting may have more to do with choke and idle mixture settings with stone cold engine.

    Press the gas pedal to the floor three times to allow the accelerator pump to dump a big shot of fuel into the intake immediately before turning it over to see if it helps alleviate the hard starting. This is a common technique on a carbed engine with a choke that isn't working well to get it started.
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    Or the seals are shot and the bowls are leaking down (I've got a Q-Jet in need of a rebuild for this very reason).

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    Good point. I'm not familiar enough with the 4.2 carb to know if there are sealing surfaces for the float bowl below the fuel level. If that is the case, there should be some evidence of external fuel leakage around the carb and intake.

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    Looks like a leak. Any idea what kind of carb?

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    Quote Originally Posted by Midlifecrisis View Post
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    Looks like a leak. Any idea what kind of carb?
    Looks like a Weber 32/36 to me.
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    Ya , it's a Weber. Also notorious for fuel siphoning back to the tank. Some people have used a check valve to alleviate the issue or switched to a low pressure high volume electric pump.

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    AHHHHH!! Work is killing me. I want to sort this out so I can play in the snow.
    I fix aircraft for a living and I usually start simple. That being said. A complete carb rebuild sounds daunting.
    If its the fuel pump or I need to put a loop in the fuel line leading to the carb (gravity) will I find fuel in the filter?
    If I find fuel in the line, is it the carb leaking?
    I am assuming the fuel pump has a check valve in it and maybe its running back into the tank?
    By the way you guys are awesome.

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    Go with the rebuild. Takes about an hour and a half ish. Videos on YouTube give you a step by step guide through it.
    It also calls for beer.

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    Quote Originally Posted by gnomeo View Post
    Go with the rebuild. Takes about an hour and a half ish. Videos on YouTube give you a step by step guide through it.
    It also calls for beer.
    I started looking at my choke. It's electronic.
    She wasn't activating. A bit of sandpaper on the terminals and viola.
    Thanks everyone for the tips.

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    Well I may have jumped the gun a bit. She was a bit of beast again this morning. I still think fuel is running back to the tank.
    Has anyone tried putting a check valve on a fuel line? And if so, which one? Before the filter or after?

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    I haven't done that yet but i have the same problem.
    Ill figure that out when i switch to electric fuel pump and fuel cell.
    I have heard though that the seal on the mechanical fuel pump can lead to drain back. Dont know how true that is though.

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    Quote Originally Posted by gnomeo View Post
    I haven't done that yet but i have the same problem.
    Ill figure that out when i switch to electric fuel pump and fuel cell.
    I have heard though that the seal on the mechanical fuel pump can lead to drain back. Dont know how true that is though.
    Well it turns out it was a problem with my choke after all. Took it off. Tested. Calibrated. Works.

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