Carter WDO carb advice for improving fuel economy in Technical Posted July 26 Do as Carbking says. Set your metering rods to factory. You will also need to raise you float height to nearly an 1/8th Over factory settings as modern fuel has a way less Specific Gravity. ( you’ll be running rich at factory settings. ) . Then use a vacuum gauge to set you air screw to the maximum vacuum you can get. The adjust your timing to get maximum vacuum again. Then go back and do the air screw on more time. Then do the timing one last time to get maximum vacuum. Once this is achieved, retard timing by one column. a quality Vacuum gauge with a big dial is best. This method is by far the best way to tune those Carbs and your timing. Ask any Hudson guy. good luck.