[speedytang]

First thing is your probably running to much fuel pressure and since the engine came from a yard it is probably been beat on. The best thing is to remove the valve covers and check to see if the rockers are tight and look for cracked rockers or a push rod hitting the side of a rocker. Use cardboard to make a shield because oil will be spraying all of the place but you can run the engine and hear which cylinder is giving you a problem.