If the power valve has a torn diaphragm, it will leak excess gas into the intake at idle, causing the engine to idle too rich.
To determine which power valve your car needs, you need an accurate vacuum gauge that you can read while driving. When you accelerate, watch the gauge to see what the reading is when the engine bogs or hesitates during acceleration. Then, select a power valve that is numerically higher than the reading when it bogs. So, if the engine bogs at a reading of "6", you need a 6.5 power valve.
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