As you open the throttle, more air enters the engine and manifold pressure rises accordingly.
The ECU is watching the manifold pressure and rpm to determine how much fuel to give the engine.
If you delay the pressure signal to the MAP sensor that the ECU is watching, the ECUs response with additional fuel will also be delayed.
As you add restriction to the pressure signal to the MAP sensor in the effort to dampen the signal you are adding a delay to the fuel response. At some point as you add more restriction, the fuel response will be delayed enough to cause the engine to go lean momentarily as you open the throttle. In the worst case this could cause an engine stumble.
The accelerator pump function can help solve this to some extent.
Every engine is a little different.
The .040" orifice in the sump adapter works fine on most engines.
If the MAP signal is unstable, the .020" orifice adapters can be installed.