Black soot indicates an overly rich condition on the carb. The bog on acceleration would indicate the secondaries are opeing too soon, this is adjusted by changing the spring in the vaccuum chamber for the secondaries. The idle problem could be a vaccuum leak, check for that with a spray can of carb cleaner. Spray small squirts of it around the carb base, and all the other sources of possible leaks. There's a lot of good books available on tuning Holley carbs that are far better than a Haynes rag.