IS it the carb adjustment OR the spark plugs

[rockfla]

On my bone stock 39 Merc Flathead.......I checked all my plugs the other day to see just how its running......the two back cylinders the plugs are "black" and running rich, the other six are burning perfectly......thoughts????

[scicala]

If they are black and shiny/wet looking it could be oil. See if they smell like burnt oil.
Maybe clean all the plugs and run it for a while to check again.

Sal

[rockfla]

The back two are "sooty" black!! Not shinny wet black!!

[Tinker]

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It's just how airflow works. On a single carb the air flow is limited to the outside cylinders. Run the others lite or clean the plugs more often. Heat of the motor will help.



shiney black is to much fuel. Somewhere around brown is good. Best of luck with that.