I have a 305 chevy engine in a ski boat with a holley 650 double pumper mechanical secondary carb. Yes I know this carb is way too big for the engine, but I needed a carb and bolted on one I already had. When standing behind it idling, you smell alot of gas. I adjusted the two small needles located on the primary metering block, to achieve max vacuum. I had the idle down low and verified the primary butterflies were closed. Turning the screws had very little effect on the vacuum gauge. If my power valve was blown would it act this way? I also checked the float levels on both bowls, they were correct. The carb won't adjust out. Thanks.