Carbon fouled plugs except #5 - Chevy Nova Forum
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Old 13th-May-2019, 08:02 PM   #1
Carnot
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Carbon fouled plugs except #5

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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Old 14th-May-2019, 06:43 AM   #2
bracketchev70

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Seems odd that one cylinder runs better. What I would think is possible gas washing to "clean" that plug. I would be checking intake gaskets to see if its sucking oil in from the valley.
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Old 14th-May-2019, 12:13 PM   #3
pockets

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Your wideband is not reading correctly for sure.

Gap the plugs at .040", put new TR4 or TR5 plugs in.

Verify the float is set right.

What is your initial timing, and when is all the timing advanced by (rpm), how many degrees centrifugal.
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Old 15th-May-2019, 10:16 AM   #4
Carnot
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Thank you for the suggestions, maybe this is a float issue. I will also try the plugs you suggested and a slightly tighter gap, I was running .042".

Initial timing is 10degrees with another 20degrees of advance coming in by ~2500rpm.
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Old 15th-May-2019, 12:05 PM   #5
pockets

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Bump your timing up 4 more degrees to 34 total.
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Old 16th-May-2019, 09:22 AM   #6
ism deuce

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Carb Adjustment

Spark plug color indicates gas fouling. Adjust idle mixture screws with vacuum gage and tachometer.
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