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Can l go to a hotter plug if my plugs are all blackened.
You can but before you do you should figure out what exactly is blackening them or the new plugs will look the same. Blackened from what? Take some pics.
Probably not because they are a heat range too cold. Possibly choke staying on, carb bleeding over due to too much fuel pressure or a bad needle and seat and/or float with a hole in it. Holley carbs with a blown power valve can run rich as well. A slim chance you could have a bad coil. Slim possibility.
............Or you checked them before they had time to normalize or the engine cooling system has a problem and is running under temperature