Need Help With Engine Diagnosis

These engines when new were expected to have the carburetor rebuilt at least once every few years. I recommend a rebuild at least once every 10K miles, every two years for a Holley, and at least once a year cleaning of the reusable air filter if you have one. You'd be amazed how much crap ends up in the air bleeds and little passages even with a good air filter, nevermind something high-flow.