[Oldsguy]

The reason the booster affects engine performance is that it is a big storage device for engine vacuum. If it leaks then you essentially have a vacuum leak in you engine just as if one of the vacuum lines were leaky or not connected on top of the manifold. This faulty vacuum messes up the operation of the carburetor since it operates on pressure differential between the engine and the ambient pressure (vacuum). And, secondly, the weak vacuum signal affects your advance unit on your distributor so you have incorrect timing advance.