With respect to the turbulence and an air filter:
In David Vizard's excellent book "Tuning BL's A-Series engine" he cites an example of a downdraft Weber carb sticking through the bonnet of a Mini. It worked terrible. They put on an air filter and a scoop and the problem went away. Seemed to be reducing the turbulence over the carb mouth was the key, and the air filter helped a lot there.

Plus there are all the other benefits of an air filter.