67 427/435 backfire. - NCRS Discussion Boards

67 427/435 backfire.

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  • Richard S.
    Very Frequent User
    • November 1, 1994
    • 809

    67 427/435 backfire.

    I drove the car for about an hour....parked it for four hours and when it came time to start her up to go home, I pumped the pedal once and then turned the key. I got a backfire out of the drivers side exhaust sidepipe. Then it started fine with the next turn of the key. What can I do to correct this potentially harmful backfire from happening again. Thanks for the help.
  • Mike M.
    NCRS Past President
    • May 31, 1974
    • 8365

    #2
    Re: 67 427/435 backfire.

    go over the ignition again. most backfires are ignition in origin. mike

    Comment

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

      #3
      Re: 67 427/435 backfire.

      Carbureted engines can do weird things, but as drivers we have some control over their behavior based on the starting procedure we use.

      If the engine was only off for an hour it was not fully "cold", so use of the cold start procedure - one pump of the throttle pedal to provide an accelerator pump shot and set the choke is not necessary. For such a "semi-cold" start I would recommend pushing the throttle open halfway and then cranking. It takes probably on the order of two to four hours, depending on ambient temperature, for and engine to be considered fully cold.

      It's possible that one cylinder had an overrich mixture that failed to ignite in the cylinder, and then it ignited in the exhaust system when it encountered the hot exhaust gas from a nearly cylinder. This would cause the AFTERFIRE (not backfire) you observed.

      If it doesn't become a recurring anamoly, I wouldn't worry about it, but don't use the cold start engine procedure after only an hour of soak in mild weather.

      Duke

      Comment

      • John Walker

        #4
        Re: 67 427/435 backfire.

        So, Duke, what was the old rule of thumb about, too lean, backfires through the carb, too rich backfires through the exhaust. I have a 454 H.O. with 750 road demon and when warmed up, if you step on the pedal briskly it will pop through the carb once and then run fine. Timing maybe?

        Thanks in advance John

        Comment

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

          #5
          Re: 67 427/435 backfire.

          Backfire through the carb can be either an ignition problem or a lean condition. If it only happens when you open the throttle, a bigger accelerator pump shot will probably solve it.

          Duke

          Comment

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