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AMC 304 mechanical fuel pump question

Discussion in 'Intermediate CJ-5/6/7/8' started by '72CJ5, Aug 4, 2012.

  1. Aug 4, 2012
    '72CJ5

    '72CJ5 Member

    Modesto,...
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    May 12, 2010
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    Right before I started my build, my fuel filter (small clear one) plugged up on me and jeep wouldn't run so in order to get home, I replaced with a straight piece of fuel line as a temp fix. Today, I put in a new fuel filter and started the jeep. Now granted the jeep is running poorly (awaiting a special delivery!) the jeep has ALWAYS kept the fuel filter full of fuel. Once in a while you would get a bubble but it was always full unless parked all night long. I started the jeep and was standing next to the engine so I could keep it running by hand and noticed that my fuel is just barely trickling into the filter...not full, but just enough to keep the bottom 1/8th of the filter full. Now my question is this, if a mechanical pump goes out, will the engine itself pull fuel from the tank? Even that super small amount? I always thought that if one goes out...its out, so not sure what to think and would like your guys input. Also checked all of my fuel lines and connections and all is good. Even removed the fuel cap to see if maybe the tank wasn't venting but all was good. Thanks ahead of time.
     
  2. Aug 4, 2012
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Nope. The only way fuel will go to the carburetor is if it's pumped there.
     
  3. Aug 4, 2012
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Mechanical fuel pumps don't typically go out 100% which is why we have pressure and volume tests for them. Sounds like you have a pump failing or a restriction in the system before the pump.


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  4. Aug 5, 2012
    '72CJ5

    '72CJ5 Member

    Modesto,...
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    Im going to blow out my lines in the next few days. I will also prob just buy a new pump since the one on it looks like it is the stock pump. Only like $30 or so.
     
  5. Aug 5, 2012
    OleBlue

    OleBlue Sponsor

    Tennessee
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    If you get a replacement, the Carter has the same diameter diaphragm as stock, or close to it. I got it from Summitt Racing. I originally picked up whatever brand Oreillys had, and it was bigger in diameter and mashed the lower coolant hose even more.
     
  6. Aug 5, 2012
    '72CJ5

    '72CJ5 Member

    Modesto,...
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    Ok, thanks alot. Are they around the same price?
     
  7. Aug 5, 2012
    OleBlue

    OleBlue Sponsor

    Tennessee
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    Yes.
     
  8. Aug 5, 2012
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    Very fine grit can form around the small flap valve inside the fuel pump rendering it inop. If you can blow both ways through the pump then the valve is not seating properly. I spray chem-tool or carb cleaner into the pump in the direction of fuel flow and then blow it out with compressed air. Re-check if you can now blow in only one direction, then your pump will work.
     
  9. Aug 5, 2012
    '72CJ5

    '72CJ5 Member

    Modesto,...
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    I havn't blown it out yet nor have I before so I dont know if it will pass in both directions. Today, I switched out my carburetors and fired up the jeep and the pump seems to be pumping fine now, keeping the filter full. I did notice though, that the fuel inside the filter is super dark and if you tap the filter, you can see this super super fine, black dust float off of it. No idea what it could be since I had pulled my fuel tank out and cleaned it really really good...super fine rust dust possible? Since my tank has a crack anyways, im just going to wait it out and buy a brand new STEEL tank. I originally bought a polly tank, but the sender area was different and there were no vent tubes coming from it so i turned it into a fuel tank for my boat.
     
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