Hi Alan------------The correct gap for Z plugs is around .044. That's assuming the engine is in stock condition and is not turbo or supercharged or equipped with a "hot" ignition system. If the plugs are dry and black, this indicates fuel fouling from a too-rich condition. If they're wet and black, oil fouling is the cause. If you're running the stock '74 flat top carbs, you will probably have difficulty setting the fuel/air mixture ratio. The standard suggestion here is to swap the stock carbs for '70 to '72 round top SU carbs. And finally--yes, the choke increases idle speed by richening the mixture. Hope this helps.