exhaust back fire

1969 CHEVROLET
7,500 MILES • 5.3L • V8 • 2WD • AUTOMATIC
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SOLEMAN
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  • 1 POST
my 1969 chevy c 10 back fires when your driving at a steady cruising speed, its fine while accelerating or decelerating and has all its power but once you hit a steady constant speed it starts to back fire. I have changed all plugs, plug wires, distributer cap check for air leaks ,
was told it might be my cam but then if it was the cam would it not back fire all the time as this is not a steady back fire. motor was just rebuilt 7500 km's ago and just recently started doing this only thing that wasn't new on the rebuild was the holley 650 double pumper that was put on it....
Could it be the carb or the MSD ignition box.
Feb 9, 2016 at 10:47 AM
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HMAC300
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check for a bad cam if it wasn't lubed on lobes and old lifters were used or new lifters with old cam lobe probably worn off, typical of chevys that era. it will do exactly like you say,pull valve covers and look for one of the valves not moving up and down like the rest also check rocker adjustment may be that as well.
Feb 9, 2016 at 12:11 PM