Here's what I do with my EBU carbs. PRIOR TO installing a carb back on the car after I have done a rebuild, I always set the carb on an open tuna fish can, on a level table. I fill the float bowl with enough gas just to fill the bottom of the float bowl. This can be done with the carb completely assembled by getting another tuna can, bending a spout in it, pouring some gasoline in the can, then use it to pour gasoline carefully down the little air bleed tube sticking up in the carb throat. That tube opens into the float chamber. Now, let it sit overnight. Next day, come out and see if the tuna can that the carb is sitting on has gas in it. If it does, you are leaking gas. Take the valve body off the bottom of the carb. If the power valve vacuum chamber in the valve body is wet, your power valve gasket leaks. Maybe wrong gasket. Maybe lousy gasket material. Maybe the mounting surface of the power valve at the bottom of the main body is scored so bad, that it will leak unless you send it to Sal Cicala, so he can buff it out for you and fix it right.