Don’t know about four strokes but:

We modify two stroke engines in several ways fundamental to carburetor operation.

The most serious is the removal of the air filter and air box (plenum chamber). Two stroke engines are always pulsing air at the carburetor inlet. The prop wash and air flow across the carb inlet carries a large portion of the fuel charge away. The fuel charge is not carried away in chainsaw configuration. On a high humidity night shining car lights on an idling engine will allow one to see the halo (looks like a smoke ring) being forced out and back in the carb. It is an interesting phenomenon to watch. Much of the fuel charge is lost to the air stream.

A velocity stack helped my engine, which is also open to the air stream. Also an air filter or plenum chamber probably would have helped.

Engines with cowls probably don’t loose as much charge. You will probably fine the velocity stack needs to point straight out.