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Engine runs poorly

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  • Tom Sarno

    Engine runs poorly

    When I attempted to start my car new car, 1972 small block that sat for approx. a year. It had a leaky fuel bowl so I used a Holly renew kit and replaced all of the gaskets. Most were shrunken and split. When I reinstalled the carb it fired right up and idled perfect for about 3 minuets then started to pop into the exhaust. It lets of a single pop or two consecutive quick pops every 15 to 20 seconds on the passenger side only.

    It also has very black, sooty exhaust coming from both tailpipes. The cap, rotor wires and plugs are good and the firing order is correct. I have never had to trouble shoot a car sat and was wondering if there is a common problem I am over looking.

    Thanks
    Tom
  • Jim T.
    Expired
    • March 1, 1993
    • 5351

    #2
    Re: Engine runs poorly

    I would also check the power valve, inexpensive, usually less than $6 at Auto Zone, have to know what vacuum rating you want. Look on the old one and it should have the number stamped on it, replace it with the same mumber.
    Since your gaskets are so new, you should be able to separate the fuel bowl and metering block without tearing the gaskets.

    Comment

    • Jim T.
      Expired
      • March 1, 1993
      • 5351

      #3
      Re: Engine runs poorly

      I would also check the power valve, inexpensive, usually less than $6 at Auto Zone, have to know what vacuum rating you want. Look on the old one and it should have the number stamped on it, replace it with the same mumber.
      Since your gaskets are so new, you should be able to separate the fuel bowl and metering block without tearing the gaskets.

      Comment

      • Duke W.
        Beyond Control Poster
        • January 1, 1993
        • 15610

        #4
        Re: Engine runs poorly

        Run compression and/or leak down tests. Afterfiring can be a sign of a leaky exhaust valve.

        Duke

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15610

          #5
          Re: Engine runs poorly

          Run compression and/or leak down tests. Afterfiring can be a sign of a leaky exhaust valve.

          Duke

          Comment

          • Gary S.
            Extremely Frequent Poster
            • July 31, 1992
            • 1628

            #6
            Re: Engine runs poorly

            I would venture a guess that perhaps you have a stuck float and the black soot is indicative of too rich a setting caused by the stuck float. In addition, the brass (?) float on my 66 Holley developed a leak and some gas got into it. It therefore registered incorrectly, affecting the idle quality. I discovered it when I disassembled the side bowls (again) and took it all apart. I picked up the float and heard/felt fuel sloshing around in it.
            Gary

            Comment

            • Gary S.
              Extremely Frequent Poster
              • July 31, 1992
              • 1628

              #7
              Re: Engine runs poorly

              I would venture a guess that perhaps you have a stuck float and the black soot is indicative of too rich a setting caused by the stuck float. In addition, the brass (?) float on my 66 Holley developed a leak and some gas got into it. It therefore registered incorrectly, affecting the idle quality. I discovered it when I disassembled the side bowls (again) and took it all apart. I picked up the float and heard/felt fuel sloshing around in it.
              Gary

              Comment

              • Jack H.
                Extremely Frequent Poster
                • April 1, 1990
                • 9906

                #8
                Add-on

                I like Duke's thinking here.... If car sat for a long time in a humid area, the problem could be temporary. Remember, on engine shut down, by random chance the valves are going to sit in all combinations (closed/closed, open/closed, closed open). You could have rust/pit build up that's preventing a given valve from fully seating that will 'go away' with some engine run time.

                But, if symptoms don't disappear RAPIDLY (say an hour or so of running), it's time to put science to work. The 'leak down' or trickle down tests Duke suggested ARE the way to go. Competent mechanic can diagnose the relative health of individual piston ring/cylinder wall as well as intake and exhaust valve seating by specfic cylinder with this test. That'll let you know proto where the engine is generically healthy vs. in need of 'watching' or immediate overhaul/repair....

                Comment

                • Jack H.
                  Extremely Frequent Poster
                  • April 1, 1990
                  • 9906

                  #9
                  Add-on

                  I like Duke's thinking here.... If car sat for a long time in a humid area, the problem could be temporary. Remember, on engine shut down, by random chance the valves are going to sit in all combinations (closed/closed, open/closed, closed open). You could have rust/pit build up that's preventing a given valve from fully seating that will 'go away' with some engine run time.

                  But, if symptoms don't disappear RAPIDLY (say an hour or so of running), it's time to put science to work. The 'leak down' or trickle down tests Duke suggested ARE the way to go. Competent mechanic can diagnose the relative health of individual piston ring/cylinder wall as well as intake and exhaust valve seating by specfic cylinder with this test. That'll let you know proto where the engine is generically healthy vs. in need of 'watching' or immediate overhaul/repair....

                  Comment

                  • Clem Z.
                    Expired
                    • January 1, 2006
                    • 9427

                    #10
                    Re: Engine runs poorly

                    the big problem with older holleys is a warped metering body or main body. you need a short straight edge the check them. the main body can be filed flat but the metering bodys must be straighten with a jig.

                    Comment

                    • Clem Z.
                      Expired
                      • January 1, 2006
                      • 9427

                      #11
                      Re: Engine runs poorly

                      the big problem with older holleys is a warped metering body or main body. you need a short straight edge the check them. the main body can be filed flat but the metering bodys must be straighten with a jig.

                      Comment

                      • Clem Z.
                        Expired
                        • January 1, 2006
                        • 9427

                        #12
                        Re: Engine runs poorly

                        to repair a leaking float,just put it in boiling water and the gas will boil out plus you will see were the leak is and then you can solder it shut.

                        Comment

                        • Clem Z.
                          Expired
                          • January 1, 2006
                          • 9427

                          #13
                          Re: Engine runs poorly

                          to repair a leaking float,just put it in boiling water and the gas will boil out plus you will see were the leak is and then you can solder it shut.

                          Comment

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