I've got a zz4 motor with a standard HEI and a 600 cfm edelbrock carb. The motor is currently fouling plugs within 50 miles of putting new plugs in. They all appear carbon fouled with the exception of #5 which looks carbon fouled on the bottom but shiny clean on the top. The carb is at factory settings and my narrow band air fuel gauge indicates it's running at stoich or lean but the plugs tell a different story. Could this be a vacuum leak issue close to the #5 intake runner? Thanks for any suggestions.
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