ponkotsu, where are you getting your vacuum reading? If you are referencing manifold vacuum, your statement is wrong.The higher the manifold vacuum, less open throttle, the easier the engine is working, thus better fuel economy. If you are getting vacuum from the ported vacuum source from the carburetor,IE, venturi vacuum, then you are correct. Higher vacuum from the ported source means the engine is pulling harder, wider open throttle, thus less fuel economy. On todays fuel injected engines the vacuum source would be from the manifold. try it. Hook a vacuum gauge to a manifold vacuum source and note the vacuum at idle will be about 20" vacuum, depending on altitude and engine condition. Open the throttle, and watch the vacuum fall. using the same hook up, drive and watch the vacuum fall whenever you open the throttle, however slightly. Then watch it rise whenever you close the throttle and are coasting.
