The car is running rich. Carbon-fouled spark plugs are all dark black and smell like raw fuel in my garage.
It can always be a challenge when addressing an issue with a classic car, such as with your 68’ Chevelle. Provided that your Chevy has not been modified, your problem may simply be found in the spark plugs. Each spark plug is designed with a specific purpose and some spark plugs run hotter while others run colder, depending on engine needs. Switching over to a hotter spark plug may clear up your Chevelle issues. However, it is also a possibility that the carburetor needs to be serviced or adjusted. In order to be 100% certain, I would recommend enlisting the help of a certified mechanic to come by and inspect your Chevy. They will have the knowledge necessary to identify why your Chevelle is running rich as well as make the necessary adjustments or repairs to keep your Chevy on the road.
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