Power Valve Bad?

I had a bad backfire when setting up timing and have not been able to tune the carb right since. It is a new quick fuel and even though it is supposed to handle a backfire I think the power valve may have blown.
The exhaust smells super rich and if I stop the car real fast it will almost stall the engine.
I tried to test by turning idle/mixture screw in and the left side made no change. When I turned in the right side the engine quit. Supposedly if the engine quits when turning in idle mix screw then the power valve is working.

Does anyone know if the engine should quit when only one screw is turned in? When I turn in the left side nothing happens and makes me beleive that the power valve is blown.