340 engine isn’t getting enough gas, why?

Discussion in 'Small Block Mopar Engine' started by Dakota Smith, May 13, 2018.

  1. Dakota Smith

    Dakota Smith 1976 340 Feather Duster

    Messages:
    102
    Likes Received:
    13
    Joined:
    Feb 17, 2018
    Location:
    Georgia
    Local Time:
    10:30 AM
    In the last couple of weeks my 76 340 Plymouth Duster has been severely lacking in power once I get to 3rd gear. I guess there is something preventing enough gas into the carburetor, but I am not sure what it is. Everything is brand new from the fuel tank all the way to the carb, but the carb isn’t new. When spraying brake fluid around the carb while the engine was running, I noticed air is escaping from somewhere around the carb. Could changing the carb gasket be the problem or do you guys have any other suggestions? Also, the fuel vent line isn’t attached to anything at the moment. It is just open under the hood. I plan on getting a charcoal canister soon.
     
  2. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

    Messages:
    3,372
    Likes Received:
    1589
    Joined:
    Feb 7, 2013
    Location:
    Phila. Pa
    Local Time:
    10:30 AM
    Could be the winter fuel and weather is contributing to your recent problems: see this post
    Carburetor trouble
     
    • Agree Agree x 1
    • j par

      j par Well-hung Member

      Messages:
      9,567
      Likes Received:
      3094
      Joined:
      Jul 2, 2014
      Location:
      Portland Oregon
      View My Photos
      Local Time:
      7:30 AM
      First off I hope the hell you're not spring break fluid around on your motor! I hope it was brake cleaner! LOL
       
      • Like Like x 1
      • j par

        j par Well-hung Member

        Messages:
        9,567
        Likes Received:
        3094
        Joined:
        Jul 2, 2014
        Location:
        Portland Oregon
        View My Photos
        Local Time:
        7:30 AM
        A fuel pressure gauge would tell you if you're running out of fuel at any certain time or getting too low on pressure.
         
        • Thanks! Thanks! x 1
        • Agree Agree x 1
        • Dakota Smith

          Dakota Smith 1976 340 Feather Duster

          Messages:
          102
          Likes Received:
          13
          Joined:
          Feb 17, 2018
          Location:
          Georgia
          Local Time:
          10:30 AM
          Yes. Haha I meant brake cleaner.
           
          • Like Like x 1
          • j par

            j par Well-hung Member

            Messages:
            9,567
            Likes Received:
            3094
            Joined:
            Jul 2, 2014
            Location:
            Portland Oregon
            View My Photos
            Local Time:
            7:30 AM
            76 340 feather duster? What you tryin to pull LOL :poke:
             
          • AJ/FormS

            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

            Messages:
            14,179
            Likes Received:
            3589
            Joined:
            Jan 19, 2014
            Location:
            South-Central Manitoba,Canada, 900ftelevation
            View My Photos
            Local Time:
            9:30 AM
            If she was going lean in third gear, there would be a lot of bucking and farting and misfiring/backfiring going on. You didn't mention any of that.

            In the absence of drama,Verify the choke is coming ALL THE WAY off:If the choke mech is not coming off, the secondaries will not open.
            After that; verify your timing systems.
            If that checks out, time for a compression test.
             
            Last edited: May 14, 2018
            • Like Like x 1
            • Dakota Smith

              Dakota Smith 1976 340 Feather Duster

              Messages:
              102
              Likes Received:
              13
              Joined:
              Feb 17, 2018
              Location:
              Georgia
              Local Time:
              10:30 AM
              What?
               
            • krazykuda

              krazykuda FABO Gold Member FABO Gold Member Technical Editor

              Messages:
              43,593
              Likes Received:
              9201
              Joined:
              Aug 20, 2007
              Location:
              Orland Park, IL
              Local Time:
              9:30 AM
              Check your fuel filters....

              The one in the tank can get old and disintegrate... The 'sock' on the end of the fuel pick-up tube is known to break down and clog the tube... Then make sure the in line fuel filter is not clogged either.... .
               
              • Agree Agree x 2
              • Like Like x 1
              • furrystump

                furrystump Well-Known Member

                Messages:
                485
                Likes Received:
                257
                Joined:
                Nov 13, 2004
                Local Time:
                3:30 PM
                So its a thermoquad? Is this a stock setup? No 340 in 76 IIRC. It would be 360 I think, but I’m old and forgetful. Pictures always help.
                 
                • Like Like x 1
                • Dakota Smith

                  Dakota Smith 1976 340 Feather Duster

                  Messages:
                  102
                  Likes Received:
                  13
                  Joined:
                  Feb 17, 2018
                  Location:
                  Georgia
                  Local Time:
                  10:30 AM
                  They’re are both brand new, so I don’t think they would be clogged.
                   
                • Dakota Smith

                  Dakota Smith 1976 340 Feather Duster

                  Messages:
                  102
                  Likes Received:
                  13
                  Joined:
                  Feb 17, 2018
                  Location:
                  Georgia
                  Local Time:
                  10:30 AM
                  The carb is a 4 barrel Edelbrock, part #1407. The original engine was a slant six, but it was swapped for a 340 before I got it.
                   
                • lil red

                  lil red Well-Known Member

                  Messages:
                  746
                  Likes Received:
                  78
                  Joined:
                  Feb 15, 2011
                  Location:
                  south shore, N.S.
                  Local Time:
                  11:30 AM
                  had this happen to me in an aspen R/T, the sock would collapse and starve for fuel...shut the car off for a few minutes, restart then it would work fine for a bit till it happened again....took a while to track that down...good call kuda
                   
                  • Like Like x 1
                  • Thanks! Thanks! x 1
                  • furrystump

                    furrystump Well-Known Member

                    Messages:
                    485
                    Likes Received:
                    257
                    Joined:
                    Nov 13, 2004
                    Local Time:
                    3:30 PM
                    So it falls on it’s face in third gear when you are at full throttle through first and second? Put a fuel pressure gauge on it. NOT a liquid filled gauge. If you still have 5lbs of fuel pressure in third it might be the needle and seat. You can empty those carbs it the motor draws enough. They make a larger needle and seat. I run them.
                     
                    • Like Like x 1
                    • nm9stheham

                      nm9stheham Well-Known Member

                      Messages:
                      9,043
                      Likes Received:
                      1741
                      Joined:
                      Dec 20, 2013
                      Location:
                      Waynesboro, VA
                      Local Time:
                      10:30 AM
                      Same sized fuel line as was there for the /6? Probably too small.

                      And what fuel pump do you have? Can be bad out of the box or if a straight stock one, running out of capacity.

                      As said, start with fuel pressure test at the carb inlet and watch the fuel pressure gauge as you get to the 'weak' speed. Ought to stay in the 5-7 psi range all the time. If it does, then yo have eliminated the lines and pump and tank and can focus on the carb.
                       
                      • Like Like x 1
                      • diymirage

                        diymirage HP@idle > hondaHP@redline FABO Gold Member

                        Messages:
                        13,659
                        Likes Received:
                        5874
                        Joined:
                        Oct 12, 2012
                        Location:
                        michigan
                        Local Time:
                        10:30 AM
                        I had the same problem with my duster
                        Turned out the little "rubber" fuel line that connects the pick up to the hard line had too much of a bend in it and would collapse on itself
                         
                        • Like Like x 2
                        • 12many

                          12many Well-Known Member

                          Messages:
                          464
                          Likes Received:
                          529
                          Joined:
                          Dec 14, 2016
                          Location:
                          South Carolina
                          Local Time:
                          9:30 AM
                          Are you sure the vent line actually vents? Checked the fuel cap?
                           
                        • rigger3006

                          rigger3006 Well-Known Member

                          Messages:
                          639
                          Likes Received:
                          124
                          Joined:
                          Aug 6, 2013
                          Location:
                          bc
                          Local Time:
                          9:30 AM
                          liquid filled fuel pressure gauge? whats wrong with them,curious?
                           
                        • furrystump

                          furrystump Well-Known Member

                          Messages:
                          485
                          Likes Received:
                          257
                          Joined:
                          Nov 13, 2004
                          Local Time:
                          3:30 PM
                          They warm up and go crazy. The fluid expands and makes the reading fluctuate. I had a liquid filled gauge that while idleing it would go from zero to 10 lbs. back to zero. I had heard about not using the fluid guage. I drained the gauge rock steady at 6lbs. Still use the gauge.
                           
                          • Like Like x 1
                          • AJ/FormS

                            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

                            Messages:
                            14,179
                            Likes Received:
                            3589
                            Joined:
                            Jan 19, 2014
                            Location:
                            South-Central Manitoba,Canada, 900ftelevation
                            View My Photos
                            Local Time:
                            9:30 AM
                            Great tip!
                            If I ever get curious about my fuel-pressure, I'll try to remember your tip.
                             
                          • T56MaxTorq

                            T56MaxTorq Well-Known Member

                            Messages:
                            796
                            Likes Received:
                            205
                            Joined:
                            Dec 21, 2010
                            Location:
                            CO
                            Local Time:
                            8:30 AM
                            I’ve found very little parts for a 45+ yo car to be new. They are all refurbished and mostly poor at that. Even aircraft parts. Since there are so many variants and aftermarket, describe your fuel system tank-carb.

                            Electric or manual pump? Regulator? Pump cam could be flat or wrong pump, cam, cover configuration. How do the filters look? Some filters you must cut open. Any kinked hardlines? Check carb float level. Tank could be full of sealant chips, you never know.

                            Thats even if this is a fuel delivery problem.

                            Posting a video would help. AJ is right, it would be fuckin pissed off and violent.